Gemstones

Cally Oldershaw

KEY TO THE CRYSTAL SYSTEM

Although there is no such thing as an ‘amorphous crystal’, we have included it in this key for identification purposes.

Amorphous

Orthorhombic

Cubic

Tetragonal

Hexagonal (six-fold symmetry)

Trigonal (three-fold symmetry)

Monoclinic

Triclinic

KEY TO THE HARDNESS SCALE

The relative hardness of each gemstone is indicated thus: H3½ represents a gemstone with a hardness rating of 3½.

INTRODUCTION

This easy-to-use guide to gemstones contains more than 130 entries (145 pages) of full-colour photographs with descriptions.

Divided into five sections, including a section on mineral gemstones and one on organic gemstones, this book guides you through the subject of gemmology and introduces you to the main gemstones used by jewellers, healers and collected by gemstone enthusiasts. There is an entry for each gemstone, plus an extra introductory page for those with more than one gemstone in the ‘family’ – for example, beryl, which includes emerald and aquamarine.

For each gemstone, there is a colour photograph to help you recognise it. Photographs of well-cut gemstones show what they look like before they are set in jewellery. There are also photographs of gemstones set in spectacular pieces, designed to show them to their best advantage. The jewellery includes historical, famous and modern pieces. Gemstones that are best polished, for example as slices for inlay or mosaic work, domed shapes (cabochons), cameos, intaglios or carvings, are illustrated with appropriate photographs.

To help you find what you are looking for, each gemstone has information along the side of the page, which includes:

a line diagram of the typical crystal shape

the name of the gemstone

the name of the gemstone ‘family’

hardness

the page number.

The text on each page tells you about each gemstone. You may want to know why the gemstone has the name that it has;for example, it may be because of its colour, where it was found or perhaps because of its chemistry.

Maybe you are interested in knowing a little of the history of the gemstone, who first found it, whether ancient civilisations held it in awe and how they used it as a decorative gemstone or perhaps even a weapon.

You might like to know about the myths and legends and the beliefs held by healers that are associated with some of the gemstones. Each gemstone has its own story to tell. This book is for you to find out some of those stories.

To help you use the book as a reference source, information is clearly shown in boxes and tables individually alongside each gemstone and at the back of the book. Turn to page 174 to find out more about what these headings mean:

name

chemical formula

crystal system

hardness

Specific Gravity (SG)

Refractive Index (RI)

Birefringence (DR)

lustre.

HISTORY AND FASCINATION OF GEMSTONES

If you have ever walked along a beach and picked up a pebble, or seen something shining or twinkling on the ground and stopped to have a look, you will know the feeling of seeing that special something that catches your eye, that you want to have a better look at, that you may want to keep.

The outcome of this fascination is that gemstones have been coveted through the ages as something special, something even worth dying for. Surrounded by myths and legends, gemstones have attained a particular significance that has lasted for centuries;from prehistoric beads and ornaments to the present-day jewels of the royal families, engagement and wedding rings worn to celebrate marriage, and the ‘bling’ worn by both men and women.

But what makes a gemstone? Gemstones have always been associated with adornment, wealth and fame. Nowadays almost any material can be used to fashion jewellery for adornment for practically any part of the body, or to adorn fashion accessories such as shoes, handbags and hats. Artists and sculptors may also use gemstones in their creations. Plastics, glass, wood and clay are used in what is termed ‘costume jewellery’, some are faceted and called ‘gems’, but are they gemstones?

GEMSTONES: ATTRIBUTES

A gemstone is defined, by jewellers and gemmologists (those who study gemstones scientifically), as having three attributes:

beauty

durability, and

rarity.

Beauty

Beauty is essential for all gemstones, as the prime objective is to have an attractive product. But, as they say: ‘Beauty is in the eye of the beholder.’ A faceted gemstone may be preferred by some, while others find more beauty in an uncut rough crystal still in its ‘natural state’.

Durability

Durability, the strength and hardness of a gemstone, determines how well it will last without becoming scratched, chipped or worn. For a gemstone to keep its sparkle, not just for months or years, but for generations, it should be tough and have a hardness of more than 7 on the Mohs’ scale (which measures the hardness of each gemstone on a scale of 1 to 10 – see p176). It should also be treated with care. Softer materials can be cut as gemstones, but care must be taken in setting them in a way that protects them from wear and tear. Only diamond, with a hardness of 10, cannot be scratched by any other gemstone. Only a diamond can scratch a diamond, which is why this gemstone is considered the most long-lasting. Organic gemstones (see pp148–173) are generally not as hard as the mineral gemstones (see pp26–147) and are fashioned accordingly.

Rarity

Rarity is a key attribute because ultimately it is the rarity that determines the value and it is the value that determines the market price of a gemstone. Rarity may refer to the rarity of the gem species, or the rarity of a particular gemstone – for example, because of a particularly rare colour, a special locality, or unusual or record-breaking size.

FAMOUS GEMSTONES

The most famous gemstones are probably those that are the record breakers – for example, the largest, the oldest or the first found. They may also be those with a fascinating or intriguing past – perhaps a story spanning many generations with tales of murder, or gemstones attributed with the properties of good or bad luck or a deathly curse. Additionally, they may be famous because of the people with whom they have become associated – for example, the Elizabeth Taylor Diamond (Taylor-Burton Diamond).

A gem may have attained fame for several reasons – for example, the Hope Diamond is famous not only for its colour (blue) but also its size, its history and that of its owners, who some believe have been cursed with bad luck as a consequence of owning the diamond.

There are tales of famous gemstones that have been re-cut or can no longer be traced;some are in private collections, others have been sold at auction to anonymous buyers and yet others have simply disappeared. The whereabouts of many, though, is still known – for example, those in the palaces or vaults of royal families, national treasuries or museum collections, and those owned by millionaires and celebrities.

Hope Diamond

Logan Sapphire

A diamond and sapphire necklace

MUSEUM COLLECTIONS

Below are just a few of the museums that have famous collections of gemstones and jewellery:

USA:the Smithsonian Institution, and the American Museum of Natural History

London, UK:the Tower of London, British Museum, Victoria and Albert Museum, and Natural History Museum

Paris, France:the Louvre

Germany:the gemstone museums of Idar-Oberstein and Dresden’s Green Vault

Istanbul, Turkey:the Topkapi Palace Museum

St Petersburg, Russia:the State Hermitage Museum.

DIAMONDS:THE 4 CS

Rough diamonds are sorted (graded) depending on their crystal shape, size and clarity before being sold to be cut and fashioned. In assessing the value of a cut diamond when buying or selling, those in the jewellery trade will take four attributes into account. These are generally referred to as the 4 Cs:

colour

cut

carat, and

clarity.

Colour

You may have heard a so-called ‘perfect’ diamond being referred to as a ‘D flawless’. This is the terminology used to describe a diamond with a colour ‘D’ (the whitest and cleanest colour) and totally clear, without any flaws or imperfections. Most diamonds, however, have a slight hint or tinge of colour, usually yellow or brown. Without training and practice, the very slight differences in colourless diamonds are difficult to see. It is not until about grade M that the yellow tinge becomes more obvious. The bright coloured diamonds (including pink, yellow, blue and green) are called fancy coloured diamonds. They are described using different colour schemes.

The GIA (Gemological Institute of America) colour grading scheme (see the table opposite) is one of those that is used by professional jewellers.

Colour grading

Description

D

Colourless

E

F

G

Nearly Colourless

H

I

J

K

Faintly Yellow

L

M

N

Very Light Yellow

O

P

Q

R

S

Light Yellow

T

U

V

W

X

Y

Z

Z+

Fancy coloured diamonds

Cut

The shape of the cut and the make of the cut (how exactly it has been cut) are taken into account when assessing the cut of a diamond. The round brilliant cut is the most popular cut for a diamond. The angles and dimensions of an ‘ideal brilliant’ are worked out mathematically (for example, by diamond cutter Marcel Tolkowsky in 1919), to give the best possible shape and number of flat polished faces (facets) to ensure that light which enters the gemstone is reflected back towards the eye of the viewer. A well-cut brilliant diamond will sparkle showing flashes of all the colours of the rainbow (fire); a badly cut one will appear dull and lack fire.

Other traditional shapes used include the step cut, rose cut, cushion cut, baguette, marquise, rectangular and square cut. With the introduction of computer technology and the use of lasers in gemstone cutting, modern cuts are far more varied, including fancy shapes such as kite, heart, cross and hexagon.

Examples of some traditional shapes for cutting diamonds

Carat

The unit of weight used to measure diamonds is the carat (0.2g) (g = gramme). The name is thought to have been derived from the carob, which is now used as a chocolate substitute. Each seed or bean of the carob is nearly identical in weight. Traditionally, a one carat diamond was the same as the weight of one carob bean, though it is now standardised as 0.2g. In the Far East, rice was used as a comparison and one carob bean equalled four grains of rice. There are 100 points in a carat, so half a carat diamond will weigh 50 points.

Clarity

The clarity grading of a diamond is an assessment of its inclusions and flaws. Internal flaws (inclusions are one type of flaw) include, for example, cracks, air bubbles and the presence of other minerals within the diamond. Surface features include scratches, chipped areas and pits, which are also assessed. Surface flaws (also called blemishes) may be caused as a result of cutting and polishing, and care should be taken to check the girdle (the widest part of the stone), which separates the top (crown) from the bottom (pavilion) of the gemstone for marks. The cleaner the diamond, the better its clarity grade and the more valuable it is.

Grading (see the table opposite) is carried out using a strong light and a ×10 magnifying lens. The grade, and therefore the value and price, are affected by the inclusions, but as no difference can be seen between a flawless diamond (categorised as F) and one with slight inclusions (categorised as SI) without the ×10 magnification, they look the same to the naked eye. It is only when the clarity reaches the grade I1 (imperfect 1) that the flaws can be seen.

Gem-testing laboratories can prepare a ‘plot’ (line drawing or sketch) of a diamond’s inclusions and include this on a diamond grading certificate. In the same way that no two people will have the same fingerprint, no two diamonds will have the same clarity plot.

Clarity Grading

Description

F

Flawless. No internal or external flaws. Extremely rare.

IF

Internally Flawless. No internal flaws, but some surface flaws. Very rare.

VVS1–VVS2

Very Very Slightly Included (two grades, VVS1 is the least included). Minute inclusions very difficult to detect under ×10 magnification by a trained gemmologist.

VS1-VS2

Very Slightly Included (two grades). Minute inclusions seen only with difficulty under ×10 magnification by a trained gemmologist.

SI1-SI2

Slightly Included (two grades). Minute inclusions more easily detected under ×10 magnification.

I1-I2-I3

Included (three grades). Inclusions visible under ×10 magnification. Inclusions also visible to the naked eye.

CAT’S-EYES AND STAR STONES

Some gemstones have oriented inclusions that reflect light in such a way that when they are cut en cabochon (as a rounded polished dome) they show a bright line or star across the surface of the gemstone. Parallel elongate, needle-like or fibrous inclusions will result in a line, also known as a cat’s-eye because of the similarity to the eye of a cat. Gemstones showing a cat’s-eye may be called chatoyant after the French word chat, meaning ‘cat’. When inclusions intersect, they may produce a star stone (the effect is called asterism). Star stones may have four, six or sometimes twelve ‘arms’ to the star.

Rosser Reeves Star Ruby

Star of Asia (sapphire)

SYNTHETIC AND SIMULATED GEMSTONES

The value and appeal of gemstones are such that those who cannot acquire the ‘real thing’ will consider the option of having something that has the appearance of the gemstone that they desire. There are records of turquoise imitations in Egyptian tombs, glass imitations of gems have been found in Roman ruins, and no doubt this practice goes back much further. With modern technologies gemstones can now be made in the laboratory.

Synthetic gemstones

Synthetic gemstones have the same chemical composition as the natural equivalent gemstone. Because of this they also have the same optical and physical properties – that is, they look the same. Corundum (sapphires and rubies) have been made synthetically in the laboratory since 1902. The Frenchman Auguste Verneuil developed the Verneuil process, melting the chemical ingredients then allowing them to cool and form a candle-shaped piece of synthetic ruby (boule), which could be faceted to imitate natural ruby. Most gemstones can be produced synthetically in the laboratory;these include:diamond, emerald, chrysoberyl, spinel, quartz and many more. Synthetic chatoyant (cat’s-eye stones) and star stones can be produced by introducing the element titanium into the process.

Simulated gemstones

Imitation gemstones can be made of any material. They do not have the same chemistry as the natural equivalent. Paste (man-made glass) has been used to imitate many gemstones. Victorian paste was coloured to imitate emerald, ruby and sapphire. A gemstone of a lesser value can also be used to imitate a more valuable gemstone, for example howlite (a white, chalky mineral) has been stained to imitate turquoise, and red garnet has been used to imitate ruby.

Man-made gemstones that have no natural equivalent, for example CZ (cubic zirconia), are called artificial gemstones or artificial man-made gemstones;they are not synthetic gemstones. CZ can be made in many different colours, and has been used to imitate diamond, ruby, sapphire, emerald and other gemstones.

Above right: Koh-i-Noor replica
Below right: Imitation emerald

GEMSTONE TREATMENTS

The majority of gems on the market are routinely enhanced or treated in some way. Some treatments are so common, such as the oiling of emeralds and the heat treatment of sapphires, that they are seldom disclosed. However, disclosure of all treatments should be encouraged and all jewellers should be aware of what they are selling. In the jewellery business, the most important asset is reputation. Reputations built up, sometimes over several generations, can be lost in an instant by not disclosing certain treatments. A gemstone should only be referred to as natural and untreated if it is just that.

Surface treatments

These treatments include waxing, oiling, enamelling, inking, foiling or covering the surface with a thin film. The treatments are carried out in order to enhance the colour of the gemstone, improve its appearance by hiding cracks or flaws, or increase its value by adding special effects (such as iridescence). Surface treatments are not permanent: oils may be lost due to drying out, and enamelling, inking and so on can be rubbed off or scratched. Therefore, extra care should be taken when handling or wearing gemstones with this type of treatment.

Shallow treatments

Diffusion treatments involve heating and introducing chemicals which affect the surface and a thin layer below the surface of a gemstone. These treatments may enhance the colour or seal porous gemstones to protect them against drying out. They may also be used to produce cat’s-eye and star stones. This type of treatment is usually permanent.

Heat treatment and irradiation

Much of the ruby, sapphire and aquamarine on the market is routinely heat treated. Heat treatment is permanent and an acceptable practice. It is used to enhance or change colour, or to improve clarity. Other gemstones that may be heat treated include:amethyst (changing its colour to the more valuable citrine) and tanzanite (to remove brown colouration and improve the vibrant blue of the gemstone).

Heat treatment may be used in conjunction with irradiation. Gemstones are irradiated with electron or gamma irradiation to improve their colour and clarity. The treatment is considered permanent, and although it may occasionally fade with time, it is unlikely that any difference will be noticeable over the lifetime of the owner. Examples include:the irradiation and heating of pale or colourless topaz to give the vibrant blues popular in jewellery;heating quartz to produce citrine, amethyst and ametrine (a gemstone comprising both amethyst and citrine);and pale pink tourmaline to the neon pink or hot pink tourmaline.

‘MINERAL’ GEMSTONES

The gemstones in this part are all minerals. Minerals are naturally occurring materials that are the building blocks of earth’s rocks. Each mineral has a unique chemical composition (chemical formula). Minerals are sorted into groups or families of gemstones depending on their chemistry and their colour.

The gemstones here are mainly those that can be cut as faceted gemstones, with many flat polished surfaces – for example, diamond, ruby and sapphire. They are generally transparent, hard-wearing and have warm or bright colours, making them attractive gemstones for use in jewellery. However, there are some gemstones – for example, azurite, fluorite, malachite and rhodochrosite – that are fairly soft and can easily be scratched.

AZURITE
Azurite

In the Middle Ages, azurite was popular as a dye and a pigment used in paints. Its name is derived from the word lajward, Persian for ‘blue’. The wonderfully rich dark blue of azurite is shown at its best in azurmalachite, alongside bands of the bright green mineral malachite. Carved or polished pieces may be waxed. This is to protect what is a fairly soft mineral from scratching.

Occurrence Mainly in copper-mining areas such as Africa, Australia, Chile, China and Russia. Azurite found in Chessy (France) is called chessylite.

BERYL
Beryl

Beryl is the name given to a group of gems which share a similar chemical composition (beryllium aluminium silicate). Beryl is colourless, but small amounts of impurities, elements called trace elements, colour the gemstones. The best known is the green emerald. Others are aquamarine (blue-green), heliodor (yellow), morganite (pink), goshenite (colourless) and the rare bixbite (red beryl).

Occurrence Beryl is found worldwide. The largest gemstones are found in igneous rocks called pegmatites. World-record gems have been found in the pegmatites of Brazil. The best emerald is found in Colombia.

AQUAMARINE

Beryl

Named after the Latin aqua (water) and mare (marine or sea), the clear-blue sea-water colour of aquamarine is a popular gemstone. Often free from inclusions and found as large crystals or pebbles, it is fairly easy to cut and a favourite with gemstone designers and engravers. Most aquamarine is heat-treated to improve its colour and remove tinges of yellow or brown caused by iron. The colour change is permanent and is an acceptable practice by those in the jewellery trade. Pale blue aquamarine can also be irradiated to darken its colour. These dark blue irradiated stones are called blue beryl. Aquamarine is the birthstone for March.

Occurrence Much of the aquamarine used in jewellery is from Brazil, particularly from Minas Gerais, an area in the southeast of the country. Aquamarines are also found in other countries, including Afghanistan, Madagascar, Mozambique, Nigeria, Pakistan and Zambia.

EMERALD

Beryl

The best known of the beryl group, the vivid green emerald colour is caused by the trace elements chromium and vanadium. The name derives from the word smargus, which means ‘green gemstone’ in Ancient Greek. Emeralds are seldom clear, but contain a miniature world of inclusions. Characteristic inclusions of certain minerals or patterns can be used to find out not just the country from which the emerald came, but also the mine. Emeralds are usually oiled with polymers and epoxies to fill cracks and inclusions and enhance the colour and appearance of the stone. They should be re-oiled every few years, and should not be cleaned using ultrasound cleaners. Emerald is the birthstone for May.

Occurrence The Colombian mines of Chivor and Muzo are famous for their emeralds. The Coscuez mines are the largest source of Colombian emeralds, with as much as 50 per cent of all emeralds coming from Colombia. Other sources include Afghanistan, Bahaia in Brazil, the Copperbelt of Zambia and North Carolina (USA).

GOSHENITE

Beryl

Goshenite is colourless because it doesn’t have sufficient trace elements (impurities) to colour it. Named after Goshen, Hampshire County, Massachusetts, in the USA, where it was first found, goshenite is also known as white beryl or lucid beryl. The Ancient Greeks fashioned spectacle lenses from goshenite. More recently it has been used to imitate other gemstones – for example, diamond by placing silver foil behind the stone in a piece of jewellery, or emerald by using coloured foil. Goshenite, like the other beryls, can be irradiated to change its colour to blue or yellow.

Occurrence Localities include Brazil, Canada, China, Pakistan, Russia and the USA.

HELIODOR

Beryl

Named after its pale yellow or golden-yellow colour, from the Greek helios and doros, meaning ‘gift from the sun’. Heliodor was discovered in Namibia in 1910. The colour is due to traces of iron, which may also cause the stone to have a greenish yellow or brown colour. The pale yellow heliodor from Brazil is often step cut to give it a stronger colour. Beryl can be irradiated to give dark golden stones, called golden beryl or heliodorite.

Occurrence The best-quality stones are found in the Urals of Russia. Other localities include Brazil, Madagascar, Namibia, Nigeria, Ukraine and the USA.

MORGANITE

Beryl

Coloured by manganese, the bright lilac-pink beryl, morganite, was discovered in Madagascar in 1891 and named after J Pierpont Morgan (an American banker with an interest in gemstones) by George Kunz (after whom another pink gemstone, kunzite, is named). Morganite can be heat-treated to remove traces of yellow or orange caused by iron to give a more attractive and purer pink stone. Morganite is pleochroic, looking colourless when viewed from one direction and pink from another. For this reason it is important to set the stone correctly so that the best colour is seen through the front of the stone.

Occurrence Brazil, Madagascar, Namibia, Pakistan, southern California (USA) and Zimbabwe.

RED BERYL (BIXBITE)

Beryl

Red beryl is the rarest of the beryl group and is seldom seen as a cut stone because most crystals are too small to facet as gemstones. It has only been found in three places, all in the USA. Originally named after Maynard Bixby, who discovered the gemstone in 1904 in the Thomas Mountains in Utah, it has since been found in the Wah Wah Mountains, also in Utah, and the Black Mountains of southwest New Mexico. It occurs in volcanic rocks called rhyolites. The red colour is caused by manganese.

Occurrence New Mexico (USA) and Utah (USA).

MICROCRYSTALLINE QUARTZ (CHERT AND CHALCEDONY)
Microcrystalline quartz

Quartz may occur as transparent crystals such as the colourless rock crystal, purple amethyst or yellow-golden citrine (macrocrystalline), or may have crystals so small they can only be seen with the aid of a microscope (microcrystalline). Gemmologists tend to refer to all microcrystalline quartz that can be fashioned as gemstones as chalcedony. However, not all microcrystalline quartz is chalcedony. There are, in fact, two varieties of micro-crystalline quartz:chalcedony and chert. Chalcedony has a fibrous texture comprised of microscopic elongated ‘fibrous’ quartz crystals e. g. agate. Chert is comprised of more ‘granular’ microscopic quartz crystals e. g. chert, flint and jasper. Blood-stone may be either fibrous or granular. Named after Chalcedon (also known as Calchedon), an ancient port near present-day Istanbul in Turkey, chalcedony is divided, somewhat arbitrarily, into those specimens that are predominantly a solid colour or have straight bands and those that have curved lines or bands (agate). Different coloured chalcedony has different names – for example, the reddish-brown carnelian, apple-green chrysoprase or heliotrope with red spots.

Occurrence Microcrystalline quartz is found worldwide.

BANDED AGATE

Microcrystalline quartz

Agate occurs in hard nodular rocks, or geodes, which when broken open reveal chalcedony with intricate patterns of concentric banding in a wide range of colours. The nodules are found in igneous rocks and lavas. There may be a hole or a block of a single colour towards the centre of the pattern and a small pipe or exit route marked towards the edge. Agate may have curved lines or bands interspersed with bands of crystals that may be colourless quartz or coloured by impurities. Romans Pliny the Elder and the poet Silius Italicus quote in their writings that agate had been found for the first time in Sicily, in the Achates River, from which the stone took the name. Agates are given descriptive names after their appearance – for example, Cyclops agate (from Mexico), star agate and cloud agate. They may be transparent, translucent (allow light through) or opaque. Thin slices of translucent agate may be used as decorative panels in lamp shades or as wall or window hangings.

Occurrence Agate is found worldwide. The most famous historical locality is the Idar-Oberstein region of Germany, where agate has been collected since Roman times. There are records of mining in the region since 1548 and it remains a gem trading centre, but most agate is now imported from Brazil and Uruguay.

STAINED/DYED AGATE

Microcrystalline quartz

Agate may be dyed or stained to give a wide range of colours. Dyes and stains may be used to brighten the greys, browns, oranges and greens. They may also be used to colour agate bright colours that are not found in natural agates, such as the ink blue, neon blue and neon pink agate that can be seen sliced and fashioned as book ends or decorative wall or window hangings. Blue-stained agates are called Swiss lapis or false lapis after the blue lapis lazuli.

Agates have probably been stained since Roman times and maybe even before. The usual method is the sugar-acid treatment (see onyx, p46), though the range of modern synthetic dyes and stains allows for the use of modern techniques.

Occurrence Dyed/stained agates can now be found in shops and markets worldwide.

MOSS ‘AGATE’/MOCHA STONE

Microcrystalline quartz

Moss agate has a milky white, greyish to bluish white or colourless background (matrix) with mineral impurities or inclusions such as chlorite that forms greenish branchlike dendritic patterns or other plant-like patterns such as mosses, leaves and trees. Moss agate, also known as mocha stone, has black, brown or dark green mineral inclusions that resemble moss. Manganese oxides are a common inclusion in moss agate, as are iron oxides and iron hydroxides. Where inclusions resemble trees and other features of a landscape the specimen may be called landscape agate.

Occurrence Localities include Brazil, China, India, Scotland and the USA.

FORTIFICATION AGATE

Microcrystalline quartz

Fortification agate has patterns of angular lines and bands that resemble the outline of a fortress as seen from the air. Bands are generally pale greys and browns with white, though brighter colours may also be found. Margins may be crenulated (with square outlines) or have a zigzag angular outline. Ruin agate describes agate that resembles the profile outline of a town or village.

Occurrence Localities include Brazil, China, India, Madagascar, Mexico, Scotland, South Africa and the USA.

LANDSCAPE AGATE

Microcrystalline quartz

Although strictly a jasper rather than an agate, as it doesn’t usually show banding, this stone is referred to as landscape agate. Dark mineral inclusions such as iron oxides and iron hydroxides can form intricate tree and branch-like dendritic patterns, which may resemble landscapes with hills and trees. Lakes, islands and other landscape features may also be found in landscape agates. Landscape agate may be fashioned as polished or sliced pieces, mounted in picture frames or small lockets, or as carved pieces for brooches or necklaces.

Occurrence Localities include Brazil, China, Germany, India, Madagascar, Mexico, Scotland, South Africa and the USA.

FIRE AGATE

Microcrystalline quartz

The iridescent colours of fire agate are similar to the play of colour of opals. In fire agates, the patchy iridescent colours are caused by the reflection of light off layers of iron oxide minerals (goethite) within the quartz. The rainbow effect or ‘fire’ may be enhanced by cutting the piece en cabochon (with a rounded top), or by polishing as a rounded bead or irregular piece with a rounded surface. Fire agate, with its oily iridescence, has only been commercially available since the 1950s when trading of rough pieces from Mexico was established. The red colour is most sought after, while the less attractive browns and yellows are less valuable.

Occurrence Agate is found worldwide. Main localities for fire agate are Mexico and the USA, particularly Arizona.

IRIS AGATE/RAINBOW AGATE

Microcrystalline quartz

Iris agate is iridescent. Light is diffracted; it is split into the spectral colours. The spectral colours are the colours of the rainbow, which is why iris agate may also be called rainbow agate. The diffraction is a result of light being reflected from many thin parallel layers, called lamellae, which are within the quartz (chalcedony) of the gemstone. The lamellae are made up of light and dark bands of microcrystalline quartz with different properties. The light bands are made up of larger micro-crystalline crystals of quartz that spiral one way (either right or left). The darker bands are made up of smaller microcrystalline crystals that have an alternating pattern of left and right spirals. The pattern repeats itself thousands of times in these agates.

Occurrence Agate is found worldwide.

BLUE LACE AGATE

Microcrystalline quartz

The delicate lace-like patterns of blue lace agate make an attractive gemstone when polished or carved. The delicacy of the pattern and the blue colour are thought by some to instil a feeling of calm and peace, and are used to help with meditation and spiritual connection. Polished blue lace agate has been used as gemstones in brooches, pendants, necklaces and bracelets.

Occurrence Agate is found worldwide.

BULL’S-EYE AGATE/ CYCLOPS AGATE

Microcrystalline quartz

Where the agate is cut and polished to show a single ‘eye’ it may be called Bull’s-eye agate or Cyclops agate, after the one-eyed monster of Greek mythology. Cyclops agate, with the single ‘eye’ formed from concentric layers of red and white chalcedony, was found in Chihuahua, Mexico, in about 1895 by Mr. E. J. Smith, who proposed the name.

Occurrence Agate with a single ‘eye’ is found in a number of localities, including Mexico.

ONYX

Microcrystalline quartz

Onyx is a granular microcrystalline quartz and should strictly be termed chert rather than chalcedony. Onyx has straight stripes of alternating black and white or brown and white. Found mainly in Mexico, natural black onyx is rare, and much of the black onyx on the market is stained or dyed chert or chalcedony. Records show that agates have been stained by the ancient Romans and ancient Egyptians. The usual method is the sugar-acid treatment. Agate is dipped in a sugar solution which penetrates the porous rock, following cracks and flaws within the piece and the lines of the banding. The agate is then heated in sulphuric acid which carbonises the sugar, darkening it and turning it black.

Occurrence Localities include Afghanistan, Brazil, India, Madagascar, Mexico, Peru and the USA.

SARD

Microcrystalline quartz

Sard is a granular microcrystalline quartz and should strictly be termed chert rather than chalcedony. Sard is red-brown in colour and generally not as bright as carnelian (also known as cornelian) and with more of a brown tint. Sard may be imitated by soaking chalcedony with an iron solution that has the effect of staining it to give it the rust colour of sard, in much the same way as iron will rust. Named after the Greek word sardios and Latin sarda, the town of Sardis, the ancient capital of Lydia (now Turkey) where the stone was found.

Occurrence Localities include China, India, Sri Lanka and the USA.

SARDONYX

Microcrystalline quartz

Sardonyx combines the black of onyx and the red-brown of sard with the white stripes of both. Sardonyx may contain both chert and chalcedony microcrystalline quartz. Because of their layered or striped structure, sard, onyx and sardonyx are particularly well suited to being carved as cameos or intaglios. In a cameo, the image (for example, a flower) or outline of a portrait remains, while the layers that make up the background are removed. An intaglio is the opposite, with the image incised – for example, for use as a wax seal. Onyx seals were popular with the Romans.

Occurrence The Sardonyx Mountains of India remain a major source. Other localities include Australia, Brazil, China, Madagascar, Sri Lanka, the Ural Mountains of Russia, Uruguay and the USA.

CHRYSOPRASE/PRASE

Microcrystalline quartz

The translucent apple-green chalcedony popular with both the Greeks and the Romans is still the most valued chalcedony. The colour is due to the presence of nickel. The even colour and texture of chrysoprase make it ideal for use as beads and cameos. Agate has been stained to imitate chrysoprase, while the best-quality chrysoprase may look similar to jade and has been marketed as Imperial jade or Australian jade. Prase is a less bright, but far rarer, leek-green chalcedony, found in Eastern Europe and the USA. Plasma is another name given to green chalcedony, but it lacks the bright apple-green of chrysoprase.

Occurrence Historically, the finest material was mined in Poland and the Czech Republic. Since the discovery of fine chrysoprase in Queensland in 1965, Australia has become a main source. Other localities include Germany, Russia and the USA.

JASPER

Microcrystalline quartz

Jasper is the red, brown or yellow opaque massive microcrystalline quartz. Strictly a chert, coloured by iron oxides, green chlorite or actinolite, it may show a combination of colours in patches or stripes. Orbicular jasper has a gobstopper (hard spherical sweet with concentric layers) or eye-ball pattern with white or grey. Riband jasper is striped. Grey-coloured hornstone resembles the horn of a cow or ox. Ancient Egyptians, Greeks and Romans fashioned jasper as cameo and intaglio portraits, and also as beads or pieces for brooches, earrings and necklaces. Fossil wood replaced by jasper shows the growth rings, for example in the fossil forests of Arizona, USA.

Occurrence Jasper occurs worldwide, though some areas are best known for particular types of jasper – for example, the riband jasper of the Urals of Russia;red and green jasper of Kazakhstan;and the red jasper of Venezuela and India. Other localities include Chile, Egypt, Libya, UK and the USA.

CARNELIAN/CORNELIAN

Microcrystalline quartz

The orange and reddish translucent microcrystalline quartz, carnelian (also called cornelian), has been used since ancient times polished as beads or en cabochon, or fashioned as cameos or intaglios. It may be uniformly coloured or show faint banding. The major sources of carnelian are India, Brazil, Uruguay and Japan, but much of the carnelian on the market is heat-treated to improve its colour, enhancing the red and removing the brown. Carnelian has been used to ‘still the blood’ and calm the temper.

Occurrence Major sources are Brazil, India, Japan and Uruguay. Other localities include Australia, France, Germany, Madagascar, Russia, UK and the USA.

BLOODSTONE/HELIOTROPE/PLASMA

Microcrystalline quartz

Bloodstone is the green opaque microcrystalline quartz with red spots (due to iron oxides) that resemble blood, hence its name. It is also known as heliotrope. Plasma is another spotted microcrystalline quartz; it is green and opaque, but the spots are yellow or yellow-brown rather than red. Because of the blood-red spots of bloodstone, it has long been associated with blood, making athletes stronger and also stopping bleeding. In medieval times it gained religious connotations as spots were said to signify the red splashes of Christ’s blood, spilled when he was on the cross. Healing powers were then attributed to the stone and it was worn as a talisman. In Germany bloodstone is the name given to the mineral hematite, so the chalcedony is sometimes called bluestone to avoid confusion.

Occurrence India is the main locality. Other localities include Australia, Brazil, China and the USA.

CHRYSOBERYL
Chrysoberyl

Chrysoberyl occurs in a range of colours with a range of chemical compositions. Most chrysoberyl is yellow, yellowish-green, green, greenish-brown or brown. The relative hardness and high refractive index make chrysoberyl an attractive gemstone. Where the gemstone shows a cat’s-eye effect when cut en cabochon (as a cabochon) it is referred to as cat’s-eye or cymophane. Alexandrite is the best-known variety of chrysoberyl, with its wonderful colour changing from green in daylight to red in incandescent light, (for example, the artificial light of a light bulb); it is also the most valuable. The name chrysoberyl is derived from the Greek chrysos, meaning ‘golden’, and beryllos because it contains the chemical element beryllium.

Occurrence Historically, the best chrysoberyl locality was in the Urals of Russia. Other localities include Brazil, China, Myanmar, Sri Lanka, Tanzania and Zimbabwe.

ALEXANDRITE

Chrysoberyl

Alexandrite is the famous colour-change variety of chrysoberyl. The best alexandrite shows an emerald green in daylight and a ruby red in artificial light. Said to have been found in 1830 on the birthday of Tsar Alexander II and named in his honour by the mineralogist Nils Nordenskjold. The colour change is due to chromium which partly replaces aluminium in the chemical composition of the gemstone.

Occurrence The finest alexandrite was found in the Urals of Russia. More recently, discoveries in Brazil (1987), India, Tanzania and Mozambique (1993) have produced fine gemstones.

CHRYSOLITE (PALE YELLOW)

Chrysoberyl

Chrysolite is a name that has been used to describe pale yellow chrysoberyl which was popular in 18th and 19th century Portuguese jewellery and should not be confused with the pale-yellow green peridot (olivine) of the same name. Found in granites, pegmatites and schists, or recovered from alluvial sands and gravels, the hard-wearing gemstones are harder than most gemstones – only ruby, sapphire and diamond are harder. Chrysoberyl crystals may be found twinned. A particular twin associated with chrysoberyl is a triple twin or ‘trilling’, which gives the twinned crystals a hexagonal (six-sided) outline.

Occurrence Chrysolite, as with darker yellows, green and brown chrysoberyl, occurs in localities including Brazil, India, Mozambique, Myanmar, Russia, Sri Lanka, the USA and Zimbabwe.

CYMOPHANE

Chrysoberyl

Where chrysoberyl is cut en cabochon (cut as a cabochon) and shows a cat’s-eye effect (also known as chatoyancy) it may be called cymophane or cat’s-eye. Only a chrysoberyl cat’s-eye may be referred to as cat’s-eye;all other gemstones that show a cat’s-eye should be referred to using their name – for example, a sapphire cat’s-eye (or chatoyant sapphire), a quartz cat’s-eye (or chatoyant quartz), etc. The cat’s-eye effect is caused by light reflecting off parallel oriented groups of inclusions within the gemstone, which gives a thin bright line across the surface of the stone, similar to that of a cat’s-eye.

Occurrence Localities include Brazil, India, Mozambique, Myanmar, Russia, Sri Lanka, the USA and Zimbabwe.

CORUNDUM
Corundum

Corundum is famous for its rubies and sapphires. With a hardness of 9 on Mohs’ scale, only diamond is harder (10). The chemical composition of corundum is very simple, only aluminium and oxygen, and all corundum would be colourless if it did not contain small amounts of other elements – for example, ruby is coloured by the presence of chromium, and blue sapphire by iron and titanium. Ruby (red) and padparadscha (pinkish-orange) are the only members of the corundum family that have separate names;all the others are referred to as ‘fancy sapphires’ – for example, green sapphire and pink sapphire. If a gemstone is only referred to as a sapphire, it is assumed it is blue. Sapphire is one of the birthstones for September.

Occurrence Found in metamorphic rocks and in gem gravels. Localities include Afghanistan, Australia, Cambodia, China, Greece, India, Japan, Madagascar, Myanmar, Nigeria, Russia, Scotland, Sri Lanka, Thailand and the USA.

COLOURLESS SAPPHIRE

Corundum

Pure sapphire is colourless. Colourless sapphires are quite common, but most are heated to give coloured gemstones. Also, because of their relatively simple chemistry, sapphire and ruby have been made synthetically in the laboratory for more than a hundred years (1902). The different colours can be made by adding the appropriate trace elements.

Until the end of the 19th century sapphires were often given names of gems that they were similar to, with the prefix ‘oriental’. Green sapphire could be referred to as oriental emerald or oriental peridot depending on the colour. Because of the confusion this caused, it is now common practice to call all corundum (except the red, ruby) sapphire, with their colour as the prefix – for example, green sapphire. Sapphires that are not blue are often referred to as fancy sapphires. Green sapphire is therefore a fancy sapphire. The green may range from a pale green, through yellowish-green and bluish-green to dark emerald green.

In the Verneuil process, the powdered ingredients are heated so that they melt. The melt drips onto a revolving plate. As it cools it solidifies with the same chemical composition and optical properties as natural corundum. There are several methods of producing synthetic gemstones. The Verneuil method produces a candle-like shape called a boule. It can then be cut and polished. Other methods may produce synthetic gems with crystal shapes. Colourless sapphire has been known as oriental white sapphire.

Occurrence Localities include Australia, Cambodia, China, Greece, India, Japan, Madagascar, Myanmar, Russia, Scotland, Sri Lanka, Thailand and the USA. Green sapphires can be found in Africa (Tanzania), Queensland and New South Wales (Australia), Sri Lanka and Thailand.

PADPARADSCHA

Corundum

Named after the Sinhalese phrase pad ma radschen meaning the colour of the lotus flower or lotus blossom, padparadscha is a rare yellowish-pink or orange-pink coloured sapphire. The colour is caused by very small amounts of the chemical elements chromium and iron. Orange and yellow sapphires may be heat-treated or irradiated to intensify their colour.

Occurrence Sri Lanka is the main locality for fancy sapphires, including padparadscha. They have also been found in Madagascar and Vietnam. Gem quality orange and orange-brown sapphire is found in the Umba Valley in northeast Tanzania. Although it usually lacks the pink colour tinge, it is sometimes called African padparadscha.

PINK SAPPHIRE

Corundum

Pink sapphires that lack the chromium needed to give the red ruby colour still make a very attractive and hard-wearing gemstone. Although the correct name is pink sapphire, pale pinkish purple sapphire has sometimes been known as ‘oriental amethyst’, and a darker pink or purple sapphire called Bengal amethyst. To avoid confusion neither of the two names should be used. Pink sapphires are thought to protect the wearer from misfortune if worn on the skin. For this reason sapphires may be cut and fashioned so that the back of the gemstone touches the skin. A deeper cut and thicker stone will also serve to intensify the colour of a pale gemstone.

Occurrence Most sapphires are from Australia, Brazil, Madagascar, Myanmar, Sri Lanka and Thailand. Brazil is also a key producer of purple and pink sapphires.

RUBY

Corundum

The best known and most highly valued of the corundum group, ruby is red. The colour may range from pinkish-red to purplish-red and dark brownish-red depending on the amounts of the chemical elements iron, chromium and vanadium. Variations in the amount available as the gemstone is formed also lead to growth features such as lines or zones varying in colour from dark almost opaque to lighter red or almost colourless. They are strongly pleochroic and the colour is enhanced by fluorescence. The name is possibly derived from the Sanskrit word kuruvinda, or from the Latin word rubeus meaning ‘red’. Rubies are said to have the power to bring the wearer friendship and romance, energy, courage and peace. Ruby may show asterism (seen as star stones) when cut en cabochon (as a cabochon). It is the birthstone for July.

The Timur ruby and the Black Prince’s Ruby, the large red gemstone set in the front of the Imperial State Crown of the British crown jewels are in fact spinel. Although both ruby and spinel are red, they belong to different crystal systems. Rubies form as hexagonal (six-sided) crystals that may be barrel-shaped with flat or pointed (tapering) ends. Depending on colour and inclusions, the value of a good quality red spinel may be similar or more than a ruby of similar size.

The colour and quality of ruby varies with their occurrence. Mogok (Myanmar) rubies are prized for their colour and fluorescence which appears to make the rubies glow. Rubies from Sri Lanka may be paler, those from Pakistan, Afghanistan, Vietnam and Cambodia have a strong red colour and Thailand rubies may be darker red or a brownish red. The colour may be improved using heating and other treatments.

Occurrence Rubies occur in limestone and in gem gravels. Myanmar rubies are the most famous because of their colour. Other localities include Afghanistan, Australia, Cambodia, India, Kenya, Madagascar, Pakistan, Russia, Tanzania, Thailand, the USA and Vietnam.

SAPPHIRE (BLUE)

Corundum

The colour of blue sapphire is due to traces of iron and titanium. Colour variations occur, and care has to be taken when setting gemstones so that the best colour shows through the front of the gemstone. Synthetic corundum can be produced with the colour change of natural sapphire. Water sapphire is a trade name for another gemstone called iolite (cordierite) and should not be confused with sapphire. Colour can be enhanced by heat-treating, irradiation and other treatments. It is the birthstone for September.

Occurrence The most valued blue colour has come from Kashmir. Other localities include Australia, Brazil, Cambodia, Colombia, India, Kenya, Malawi, Myanmar, Nigeria, Sri Lanka, Thailand and the USA. Colour-change sapphires are mainly from Africa and Sri Lanka.

YELLOW SAPPHIRE

Corundum

Pink and yellow sapphires from Australia have been used in gemstones fashioned as floral displays in brooches and rings. With a hardness of 9 on Mohs’s scale, these bright and hard-wearing gemstones make attractive pieces. As with other sapphires, yellow sapphire used to have the prefix ‘oriental’ and was called oriental topaz. Yellow sapphires have also been known as king topaz and Indian topaz. However, as topaz is a different gemstone and in order to avoid further confusion, these names should no longer be used.

Occurrence Localities include Australia, Sri Lanka, Tanzania, Thailand and the USA.

DIAMOND
Diamond

Diamond is the most famous of all gemstones. With a hardness of 10 on Mohs’ scale, it is also the hardest material. Diamond can only be scratched by another diamond and equally, only diamond can be used to cut and polish a diamond. A lapidary, when deciding how best to fashion a diamond, will use the knowledge that hardness is a directional property, and that each diamond will have a greater hardness in one direction than another, when using diamond crystals or fragments to saw or polish a gemstone. The lapidary will also use cleavage, another directional property, in order to find the directions in which a diamond will break (cleave) along planes related to the atomic structure.

Diamond is sorted by colour, cut, clarity and carat (the unit of weight used in gemmology) – the 4Cs (see pp74–79). The value of each diamond is assessed using the results of the 4Cs. Diamond is formed of pure carbon. Its strength is due to the way that the carbon atoms are bonded in a strong 3D structure. Most diamonds are formed deep within the Earth’s crust at depths of 80–150 km (50–90 miles) and are brought to the surface as a result of volcanic explosions. Diamonds are mined from the vents and pipes of extinct volcanoes or extracted from river gravels and sands to which they have been transported during weathering and erosion of the volcanic rock (kimberlite or lamproite). Diamond is the birthstone for April.

Occurrence Diamond localities include Africa (including South Africa, Namibia, Botswana, Zaire, Ghana, Sierra Leone, Angola), Australia, Brazil, Canada, India, Indonesia, Russia and the USA.

FAMOUS DIAMONDS

Diamonds with the longest history are those found more than 2,000 years ago in the alluvial gravels of India, in Borneo and later from Brazil. It was not until 1866 that diamond was found in South Africa and diamonds were first mined from the rock in which they had formed. The earliest Indian diamonds were not cut, as it was believed this would release the soul of the gemstone and reduce its powers. The largest diamond ever discovered is the Cullinan (3,106 carats), which was found at the Premier Diamond Mine near Pretoria (South Africa) in 1870. The Cullinan was cut as nine large brilliant-cut diamonds and 96 smaller gemstones. The most famous of these is the Star of Africa diamond (530.20 carats) in the Sovereign’s Royal Sceptre of the British Crown Jewels. The Eureka’s (10.73 carats) claim to fame is that it was the first officially recorded diamond on the African continent;it was found in 1866. The discovery of the Star of South Africa (83.50 carats) in 1869 led to the South African diamond rush. The diamond in the photograph on the left is the famous Victoria-Transvaal Diamond, found in the Premier Mine in Transvaal, South Africa, in 1951. The De Beers Millennium Star (203.04 carats) is probably the most famous of recent finds, due to the amount of publicity it received as a result of the failed attempt to steal it from the Millennium Dome in London in 2000. Other famous diamonds include the Elizabeth Taylor Diamond (see page 10), the Hope Diamond (see pages 10-11) and the Koh-i-Noor Diamond (see pages 22-23).

Left: Victoria-Transvaal Diamond necklace

FANCY DIAMONDS

Hirsh diamond ring

Not all diamonds are colourless. Many famous diamonds are known not only for their size and the legends or curses with which they are associated, but also for their colour. The colour is due to the presence of trace elements such as nitrogen or boron within their structure. Diamond colours include yellow, blue, green, brown, pink, red, grey and black. Originally a marketing tool for Australian diamonds, brown diamonds are usually sold with names that describe their colour – such as cognac, sherry and champagne. The most famous fancy diamond is probably the blue Hope (45.52 carats), which is on display at the Smithsonian Institution in the USA. It is an Indian diamond, believed by many to be a cursed stone that has brought bad luck to its owners. The National Gem Collection of the Smithsonian Institution is noted for its fancy coloured diamonds. Among them are the Blue Heart Diamond (30.62 carats), along with a cognac-coloured diamond (36.73 carats), champagne-coloured Victoria-Transvaal Diamond (67.89 carats, see pp68–69), yellow Canary Diamond (12.0 carats), intense yellow Shepard Diamond (18.30 carats), intense pink diamond (2.86 carats) from Tanzania, green diamonds from South Africa and one of the largest deep red diamonds (5.03 carats) which, when purchased, was sold as a garnet. Other famous fancy coloured diamonds include the Allnatt (101.29 carats);green Dresden (45 carats) and Ocean Dream (5.51 carats);black Orlov diamond pendant (67 carats); Steinmetz pink, Moussaieff red (5.11 carats);and blue Heart of Eternity (27.64 carats).

FELDSPAR
Feldspar

Feldspar is the name given to a group of minerals that occur in rocks worldwide. Found in most igneous rocks and many metamorphic rocks, weathered feldspar is also in sedimentary rocks, sediments and soil. Feldspars are aluminium silicates. They have varying amounts of potassium, sodium and calcium, by which they are classified. Feldspar breaks along planes of weakness related to the way the atoms are arranged within the mineral (cleavage planes). There are two good directions of cleavage;one is perfect, breaking to leave a perfectly flat shining surface. Light reflecting and refracting at the surface, and diffracting from layers (lamellae) beneath the surface of different compositions, or twinning, gives the characteristic array of colours (sheen or schiller) seen at the surface in moonstone and labradorite.

Occurrence Feldspar occurs worldwide.

ORTHOCLASE FELDSPAR

Feldspar

Taken from the Greek orthos meaning ‘straight’ and kalo meaning ‘break’ or ‘cleave’, orthoclase is named because it breaks along cleavage planes to give perfect flat surfaces.

Occurrence Orthoclase feldspar occurs worldwide.

COLOURLESS ORTHOCLASE/ADULARIA

Orthoclase feldspar

Though most orthoclase is coloured by impurities, pure orthoclase is colourless. Adularia refers to the clear or transparent orthoclase with a bluish-white schiller from Adular-Bergstock in the Adula Mountains of southern Switzerland. The schiller of adularia may be referred to as adularescence, though not all adularia shows schiller. Adularia is not the same as moonstone, but the two can be confused; although both may have a similar bluish-white schiller, moonstone is generally translucent rather than clear or transparent.

Occurrence Colourless clear orthoclase occurs in Madagascar. The best-known locality for adularia is Adular-Bergstock in Switzerland.

YELLOW ORTHOCLASE

Orthoclase feldspar

The yellow colour is caused by impurities of iron in the mineral. Yellow orthoclase is fragile and can break easily. With a hardness of 6 on Mohs’ scale, it is not particularly hard-wearing. It is therefore usually only cut for gem collectors, and, when set in jewellery, a step cut or emerald cut (step cut with the corners taken off) is usually preferred. It may be cut en cabochon (as a cabochon), though this is seldom the case.

Occurrence The best yellow orthoclase is found in Madagascar. Other localities include Australia, Germany, India, Mexico, Myanmar, Sri Lanka and the USA.

MOONSTONE

Orthoclase feldspar

Moonstone is the most valuable of the orthoclase feldspars. Considered a sacred stone in India, moonstone is revered by many nationalities as a spiritual stone or dream stone, associated with healing and protection. Its moon-like appearance and characteristic blue-white schiller are caused by light reflecting off layers within the stone. The layers are alternating layers of orthoclase feldspar and albite, an end member of the plagioclase feldspars or albite with orthoclase intergrowths. Thinner and thicker layers of albite and orthoclase affect the colour and the schiller. Moonstone is usually cut en cabochon, fashioned as a cameo or carved in the shape of a moon to show its schiller to best effect.

Occurrence The best moonstone is from Myanmar and Sri Lanka. Sri Lanka is the main producer, with moonstone found both in situ and in gravels. Other localities include Brazil, India, Madagascar, Mexico, Norway, Switzerland, Tanzania and the USA.

MICROLINE (AMAZONITE)

Orthoclase feldspar

Amazonite is the name given to the blue-green gemstone variety of microcline. The characteristic colour is caused by lead and water. There may also be white, cream or yellow veins or layers of plagioclase feldspar. Translucent to opaque, amazonite is usually cut en cabochon or fashioned as small carvings. Named after the Amazon River, legend has it that native Amazonian Indians gave green stones as gifts. However, these were probably jadeite rather than amazonite. Jadeite is not known to come from the Amazon;it most likely came from Guatemala.

Occurrence India is the most important source of amazonite. Other localities include Australia, Canada, Madagascar, Mozambique, Namibia, Russia, Tanzania and the USA.

PLAGIOCLASE FELDSPAR

Plagioclase feldspar

The plagioclase series comprises feldspars that range in chemical composition from the pure sodium aluminium silicate end member (albite) to the pure calcium aluminium silicate end member (anorthite). Oligoclase is at the sodium-rich end of the plagioclase series. Plagioclase feldspars form crystals in igneous rocks and metamorphic rocks.

Occurrence Plagioclase feldspar occurs worldwide.

LABRADORITE

Plagioclase feldspar

Labradorite has the most colourful iridescence of all the feldspars. The sheen or schiller, also known as labradorescence, is due to the reflection of light off calcium and sodium-rich layers, called lamellae, within the gemstone. The flashes of colour shown by labradorite are often blue, grey and violet, but they may be any colour of the rainbow. When the full spectrum of rainbow colours is shown as the gemstone is moved, gemmologists may call this rainbow labradorite. Labradorite is named after Labrador in Newfound-land (Canada) where it was found by geologists in the 1770s. Labradorite from Finland is usually referred to as spectrolite.

Occurrence Finland, Labrador (Canada) and Norway are the best-known localities of labradorite and spectrolite. Other localities include Australia, Madagascar, Mexico, Russia and the USA.

OLIGOCLASE (SUNSTONE)

Plagioclase feldspar

Sunstone emits flashes of colour like the golden rays of the sun. Sunstone is usually opaque or translucent. Transparent sunstone is rare and when found may be faceted rather than cut en cabochon, the usual cut for sunstone. In most sunstone, the flashes of colour are due to the reflection of light off flat, platy inclusions of hematite and goethite (metallic minerals). Sunstone from Oregon (USA), known since the 1990s, has copper inclusions. Care should be taken not to confuse sunstone with goldstone, the name given to an imitation made of glass with copper inclusions.

Occurrence The best sunstone is from Norway. Other localities include Canada, India, Russia and the USA.

FLUORITE

Fluorite

The wide range of colours – including pink, yellow, colourless, green and purple – make fluorite an attractive gemstone. However, with a hardness of only 4 on Mohs’ scale and perfect cleavage, it is fragile and easily scratched. Polished beads, tumbled pieces and crystal fragments are used in jewellery. Although fluorite is found worldwide, the best known is Blue John, which is recognised by its distinctive purple or violet and creamy-white or yellow banding. Famous since Roman times, Blue John has been used to make large vases and ornaments. The name is thought to be from the French bleu jaune, meaning ‘blue yellow’, after the colours of the banding. Blue John is mined in the north of England in the Peak District National Park. Although the famous Treak Cliff Cavern and Blue John Cavern are all but mined out, small pieces are still collected in the area.

Occurrence Fluorite is found worldwide. Localities include Africa, Australia, Canada, England, France, Switzerland and the USA.

GARNET
Garnet group

Not all garnets are red. They may also be green, yellow, orange, golden, brown or black. Garnets are grouped together because they are silicates (containing the elements silicon and oxygen) and have a similar crystal structure. They vary in their chemical make-up, forming series of garnets, from one end member to another – for example, almandine garnet (iron aluminium silicate), pyrope garnet (magnesium aluminium silicate) and spessartine (manganese aluminium silicate) are end members of the iron-magnesium series, sometimes called the pyralspite series. Other garnets form the ugrandite series. Most garnets are not pure end members, but a mixture – for example, rhodolite is a mixture of pyrope and almandine. Named after the small red seeds of the pomegranate (from granatus, the Latin word for ‘seed’), garnet is the birthstone for January and the zodiac gemstone for Aquarius.

Occurrence Garnets are found worldwide.

ALMANDINE

Garnet

Almandine garnet, with a hardness of 7½ on the Mohs’ scale, is one of the hardest garnets and also one of the darkest of the red garnets (along with pyrope). Coloured by iron, almandine may be transparent or opaque. It is found in metamorphic rocks such as schist and gneiss. Named by the Roman scholar Pliny the Elder (AD 23–79) as ‘Albandicus’, possibly after Alabanda in Turkey, almandine is said to warm the heart and cure melancholy. Slices of almandine have been used in jewellery for thousands of years – for example, the Saxon treasures found in Sutton Hoo (Suffolk, UK) and in windows, including (it is said) a window or lantern on Noah’s Ark, which may have been used to guide the Ark to safety.

Occurrence Localities include India, Norway, Pakistan, Russia, Sri Lanka, Sweden and Zimbabwe.

ANDRADITE (MELANITE AND TOPAZOLITE)

Garnet

The calcium-iron andradite garnets include the yellow-green to bright green demantoid (see p86), the black melanite garnet and the yellow-orange topazolite. Topazolite crystals are found in metamorphic rocks in mountains such as the Swiss and Italian Alps, but are seldom cut as gemstones. Melanite is found in metamorphic rocks and volcanic lavas, and again seldom cut as gemstones. The type locality for andradite (the locality from which the gemstone was first discovered and described) is Drammen, in Buskerud, southern Norway. Andradite is named after B J d’Andrada, who described the gemstone in 1800.

Occurrence Localities for topazolite and melanite include Italy and Switzerland.

ANDRADITE (DEMANTOID)

Garnet

Demantoid is the best known of the andradite garnets, with its emerald green colour due to chromium and characteristic inclusions of byssolite fibres also called horsetail inclusions. Unlike most gemstones, the appearance of inclusions adds to the value of the gemstone rather than detracting from it. However, a clean stone is still more expensive than an included one. Demantoid is also one of the rarest and most sought-after gemstones. It has adamantine lustre (lustre of a diamond) and a higher dispersion than diamond, showing a rainbow-coloured sparkle or ‘fire’ masked only by the colour of the gemstone. It is named after its resemblance to diamond, from the German and Dutch word demant meaning ‘diamond’, because of its adamantine (diamond-like) lustre.

Demantoid garnets from the Urals in Russia were popular with the Russian royal family and were used in the jewellery of Faberge and Tiffany. By the end of World War 1, the source was depleted and gemstones were so scarce that mines closed. Following the discovery of a new source in Namibia in the 1990s, demantoid garnet was once again available and the public interest in this bright emerald-green gemstone was renewed. With the increased interest, the Russian sources were re-examined and small-scale production was renewed and made possible. The Namibian demantoid garnet is of a similar colour to the material from the Urals, but doesn’t have the characteristic ‘horsetail’ inclusions.

In order to make the most of its lustre and colour, gem quality demantoid is usually cut as round brilliants. Care should be taken when wearing, handling or storing demantoid as it can be easily scratched.

Occurrence The best demantoid is found in the Urals of Russia, where it was first discovered in 1868. Small-scale mining has continued since 1991. Other localities include Namibia, where it was discovered in the 1990s, Italy and Tajikistan.

GROSSULAR GARNET

Garnet

Grossular garnet has the widest range of colours of all the garnets, from colourless to pink (rosolite), orange, brown or golden (hessonite) and green (tsavorite coloured by vanadium), and from transparent to opaque crystals. There are also massive specimens (those without a crystal shape) such as Transvaal jade, pink and green grossular (crystals and massive). Transvaal jade was first discovered in the Transvaal region of South Africa and resembles jade. A recent discovery is the Mali garnet, a light yellow andradite–grossular mixture found in 1994 in Mali.

Grossular is named after the yellow-green colour of a gooseberry (botanical name Ribes grossularia). Pinkish grossular from Mexico is known as rosolite; it also occurs in South Africa and Madagascar.

Occurrence Grossular garnets are found in metamorphic rocks, alluvial deposits, gem gravels and sands. Massive grossular garnet of a gooseberry colour was first discovered in Russia and is now also found in Hungary and Italy.

HESSONITE/CINNAMON STONE (GROSSULAR)

Garnet

The orange, brown or golden colour of hessonite is due to manganese and iron. Where the colour is more like that of cinnamon, the garnet may be called cinnamon stone. Hessonite has characteristic inclusions, giving the interior of the gemstone a swirling, treacle-like appearance. Vedic astrologers believe that hessonite increases happiness and ensures a longer life.

Occurrence The best hessonite garnets are found in Sri Lanka. Other localities include Brazil, Canada, Germany, Russia and the USA.

TSAVORITE (GROSSULAR)

Garnet

Tsavorite is the most sought-after grossular garnet with its bright emerald green colour caused by the presence of vanadium. First discovered in 1967 by the Scottish geologist Campbell R Bridges in northeast Tanzania, it was named by Henry Platt of Tiffany and Company, the famous jewellers, after the Tsavo National Park in southeast Kenya. Bridges also found gem-quality crystals there in 1971, just three years later.

Occurrence Most tsavorite is from East Africa (Kenya, Tanzania and Zambia). In 1991 gem-quality tsavorite was also found in Madagascar.

PYROPE

Garnet

Named after the Greek pyropos meaning ‘fiery-eyed’, pyrope garnets are mainly found in igneous rocks. They were popular in secular jewels of the 15th and 16th centuries and have been mined for more than 5,000 years. Bohemian garnets, from near Bilin in Bohemia (in what is now the Czech Republic), were used in Bohemian jewellery, made with intricate patterns of many tightly packed small pyrope garnets. This style of jewellery was particularly fashionable in the 18th and 19th centuries and has regained popularity recently, although the garnets are now mined elsewhere. Pyrope garnets are often found as small rounded or water-worn fragments. Their blood-red colour is due to iron and chromium.

Occurrence Historically, the Czech Republic has been the main locality. Nowadays, most gem-quality pyrope garnets are from the Yakut region of Siberia and from South Africa. South African pyrope is lighter than Bohemian and has been called Cape ruby.

RHODOLITE

Garnet

A mixture of two parts pyrope to one part almandine, rhodolite garnet is found in shades of pink and red and occasionally lavender. Typically found as transparent water-worn pebbles rather than crystals, their attractive colours and lustre make them suitable as gemstones. They are named after the Greek rhodo and lithos meaning ‘rose stone’ because of their colour. A bright pink raspberry colour is the most sought-after. The name rhodolite was first used to describe pink-coloured garnets found in North Carolina, USA, in the 19th century.

Occurrence Rhodolite with the best raspberry pink colour is mined in Sri Lanka, Tanzania and Zimbabwe.

SPESSARTINE

Garnet

The manganese-rich end member of the pyralspite group. The orange-coloured spessartine, named from the region of Spessart (Bavaria, Southern Germany), has recently been found as gem quality in the Otavi region of northern Namibia. Bright orange spessartine garnets, also known as mandarin garnet because of its colour, were discovered in 1991 in Namibia, with further deposits found in Nigeria in 1994 and later in Tanzania. Malaia garnets, discovered in the mid-1960s in Tanzania, have a composition with a range between pyrope and spessartine with some almandine, and range in colour from orange to peach to reddish-orange in colour. When all three ugrandite garnets (see table on p83) are present in a gem, it may result in a colour-change garnet. Colours are said to be similar to those of the chrysoberyl variety alexandrite (see p54). However, true alexandrite shows red and green. Colour-change garnet is more usually orange-red to brownish-red, purple or bluish-grey.

Occurrence China, Germany, India, Namibia and Nigeria. Colour-change garnets are known from Madagascar and Tanzania.

UVAROVITE

Garnet

The only garnet that is always green, the colour is caused by its chromium content. It was named after Count Uvarov (1765–1855), who spent much of his life curating the gemstones of Russia, the country where uvarovite was discovered. Uvarovite generally occurs as crystals that are too small to be cut as gemstones.

Occurrence Finland, Italy, Russia, South Africa, Turkey and the USA.

HEMATITE

Hematite

Hematite has a silver-grey metallic appearance, though it may also appear black. Previously called haematite, it is named after the Greek word haem, meaning blood. This is because ground or powdered hematite is blood red. The powdered mineral has been used as a red pigment in cave art since prehistoric times. It was used as a pigment in Egyptian tombs and Roman villas, and Native Americans continue to make use of the powder to mix their war paints, worn on the body and face during traditional dances and displays. Although heavy, because of its iron content, hematite may be cut and polished en cabochon, made into small carvings, or tumbled as polished pebbles mounted in jewellery.

Occurrence Hematite from northern England and Europe was popular for use in Victorian mourning jewellery in the UK in the early 20th century. Nowadays most polished hematite is from Brazil, Canada, India and the USA.

IOLITE/CORDIERITE

Iolite/Cordierite

Found mainly as water-worn crystals and pebbles in alluvial deposits, iolite (also known as cordierite) is strongly pleochroic. It shows different colours or hues (shades) of colour when viewed from different directions. Colours seen may include an intense sapphire blue (another name for iolite is water sapphire), to a violet or insipid blue, to grey or colourless. Care must be taken by the lapidary, when the gemstone is cut, so that the best colour is seen through the front of the gemstone. It was named in 1812 after the French geologist P L A Cordier. The name iolite is from the Greek io, meaning ‘violet flower’. It is said that the Vikings used thin slices of iolite as a navigational tool because of its pleocroism.

Occurrence Main localities are Brazil, India, Madagascar, Myanmar and Sri Lanka. Other localities include Bolivia, Germany, Sweden and the USA.

JADE
Jade

Jade is the name given to two separate minerals:jadeite jade and nephrite jade. Both are tough rocks made of interlocking crystals and were thought to be the same material until 1863 when the two types were recognised. Although both | are aluminium silicates, the mineral composition is different. Both are found as water-worn river boulders and pebbles. Jadeite is the rarer of the two and is seldom found in the rocks in which it has formed (in situ). The colour of nephrite ranges from dark green (iron rich) to creamy white (magnesium rich) material, while jadeite has a far greater range of colours, including the dark to pale violet and lavender jadeite. Jadeite may have a distinctive mottling or contain black specks due to inclusions.

Occurrence The most important source of jadeite jade is Myanmar. Historically, Central America and Russia were also important. Nephrite jade occurs more widely.

JADEITE

Jade

Jadeite jade occurs in a range of colours including green, white, red, orange, black, blue, yellow, violet and the popular lavender. The best-known colour is the emerald green jadeite from Myanmar;coloured by chromium and known as imperial jade, the translucent gemstone has been supplied to Chinese carvers since the 16th century. Jadeite has also been fashioned by the ancient civilisations of South and Central America. Jadeite is usually found as river boulders. The boulders have a thick skin or ‘rind’ hiding the gemstone within. Buyers purchase the boulders, without seeing the colour of the gemstone which is hidden within, and surrounded by a thick weathered surface or ‘skin’ (occasionally a small ‘window’ is cut into the boulder).

Occurrence The main source of imperial jade is Myanmar. Historically, Guatemala and Mexico were the main sources for South and Central American Indians. Other localities include Japan, Russia and the USA.

NEPHRITE

Jade

Green to cream in colour, often with black patches, blotches or bands, nephrite jade is exceptionally tough and hard-wearing. A venerated gemstone, referred to as the ‘stone of heaven’ by the Chinese, nephrite carvings have been found in ancient burial sites and nephrite has been excavated in China since about 5,000 BC. Native North Americans from British Columbia (Canada) have carved nephrite for about 3,000 years, and nephrite carving by the Maori of New Zealand also has a long history. Tough as steel, nephrite is ideal for fashioning intricate carvings and also for use as tools. In New Zealand nephrite was used to make tools before metals were introduced by Europeans in the 18th century.

Occurrence Some of the best nephrite is mined in New Zealand. Other localities include Australia, Brazil, Canada, Mexico, Myanmar, Russia, Turkestan and, of course, China.

LAPIS LAZULI

Lapis lazuli

Lapis lazuli is a blue metamorphic rock made up of a number of minerals including dark blue lazurite, golden specks of pyrite and white veins or patches of calcite. The proportions of the different minerals give the rock its unique colour and determine its value. Lapis lazuli has been mined from the Sare-Sang mines of Afghanistan for more than 6,000 years, and has been a popular gemstone with ancient Mesopotamian, Persian, Egyptian, Roman and Greek civilisations. Still popular today, imitations include paste, stained chalcedony and imitations with a similar chemical composition such as those manufactured by the Pierre Gilson laboratory. Powdered lapis lazuli was used to make the blue pigment, ultramarine, of Renaissance art.

Occurrence The best-quality lapis lazuli is from Afghanistan. Other localities include Argentina, Canada, Chile, Italy, Russia and the USA.

LAZULITE

Lazulite

Lazulite is a rare mineral that ranges in colour from a pale blue to an intense dark blue. It could be mistaken for lapis lazuli when polished, and pale blue lazulite may be mistaken for turquoise. Lazulite occurs as small crystals in igneous rocks that may be carved or polished as beads and small decorative pieces, or cut en cabochon. Lazulite is not the same as lazurite, the blue mineral in lapis lazuli, and care should be taken not to confuse these two names. Lazulite is named after the Arabic azul, meaning ‘heaven’ (because of its blue colour), and Greek lithos meaning ‘stone’.

Occurrence Localities include Austria, Brazil, Canada, Germany, India, Italy, Pakistan, Russia, Sweden and the USA.

MALACHITE

Malachite

The distinctive banding of malachite, from a very dark green, through dark to light green, is caused by a difference in crystal size;smaller crystals give a lighter colour and larger crystals a darker colour. Malachite is found world-wide and is generally associated with the major copper-mining areas such as those of Chile and Zaire. Malachite is often found with blue azurite, the blue and green forming an attractive gemstone called azurmalachite. Valued as a gemstone since ancient times, powdered malachite has also been used as a pigment. As an ornamental stone, malachite has been used as inlay in table tops, carved as vases, bowls and statues. Large pieces have been used in buildings, carved as columns or cut as thin slabs to line walls. Banded malachite from Chessy (France) may be called chessylite.

Occurrence The most famous are the Russian deposits from the Urals. Other localities include Africa, Australia, Chile, China, Democratic Republic of Congo, France, Germany and the USA.

OPAL
Opal

Opal is a hardened silica gel which can fill fissures and cracks in rocks, as well as replacing hard parts of animals and plants, or fossils including the shell, bones or teeth. It may also replace organic material such as wood (wood opal) or form stalactites and stalagmites. Opal usually contains about 5–10 per cent water. Dehydration (drying out) may cause surface crazing (showing a cracked pattern) or the gemstone may break apart. Precious opal shows characteristic flashes of colour, called play of colour or iridescence. Opal that does not show iridescence is called potch. Romans considered opal as valuable as diamond. It has been imitated by manmade glasses such as paste and Slocum stone.

Occurrence Australia has been the main producer of opals since the 1870s. Other localities include Africa, Brazil, the Czech Republic, Honduras, Mexico, Romania and the USA.

BLACK PRECIOUS OPAL

Opal

The iridescence of precious opal is a result of the splitting of light into the colours of the rainbow (diffraction) by the regular pattern of spheres of silica which make up the opal. The colours shown depend partly on the size of the spheres, as their size determines which colours will dominate. The background colour of the precious opal may be white or pale (white precious opal), colourless (water opal), dark, or the most valuable, black precious opal, which is also the rarest of the precious opals. Precious opal is usually cut en cabochon for rings or as small polished pieces for brooches, earrings and necklaces. Black opal is one of the birthstones for October.

Occurrence Lightning Ridge, New South Wales (Australia) is the best-known source of black precious opal. Other localities include Humboldt County, Nevada (USA) and Hungary.

FIRE OPAL

Opal

Fire opal is a transparent to semi-translucent gemstone. It may show the play of colour of precious opal. The best material is transparent and is usually faceted. Colour may range from a pale yellowish-orange, to orange and dark cherry red. Fire opal may be the colour of amber, but with a hardness of 6 on the Mohs’ scale. It should not be confused with the softer organic material, as amber has a hardness of only about 2½ on Mohs’ scale. Fire opal is one of the birthstones for October.

Occurrence The best fire opal is from the Hildago region of southern Mexico. Other localities include Honduras, Kazakhstan and Romania.

OPALISED FOSSIL

Opal

Organic material such as bone, tooth or shell may be replaced by opal. Slices and tumbled pebbles of opalised wood may be used as decorative pieces in jewellery and as inlay in table tops and other decorative pieces. Opalised shell may be mounted in a necklace, brooch or pendant. Complete skeletons of fossils such as dinosaurs have been discovered replaced by opal.

Occurrence Opalised shell and bone have been found in Australia. Opalised wood is famous from the fossil forests of the USA, including Arizona, Colorado, Georgia, Oregon, Washington and Yellowstone National Park (Wyoming). Wood opal is also found in Sardinia, Italy.

WHITE PRECIOUS OPAL

Opal

As with black precious opal, white precious opal shows the play of colour (iridescence) due to diffraction of light off the regular pattern of spheres of which it is made. The body colour of the opal is pale, creamy white, or white. Opal has a hardness of 6 on Mohs’ scale, and care should be taken both in wearing the stone and in storage so that it is not scratched by harder gemstones. Care should also be taken to avoid an opal drying out, which will lead to damage – including crazing (cracking) of the surface or the gemstone breaking.

Occurrence The most famous localities for white precious opal are Lightning Ridge (New South Wales, Australia) and the opal mines of Coober Pedy (South Australia), where opal miners live underground to avoid the heat of the day. Other localities include Brazil, the Czech Republic and the USA.

PERIDOT

Peridot

Peridot is the name given to gem-quality specimens of the mineral forsterite. It is always green, although the colour may range from a yellowish-green to a dark olive green, as the colour is caused by the iron that forms part of its chemical composition. Peridot may have an oily or greasy surface appearance (lustre). It has a high bire-fringence and doubling of the facets can be seen through larger specimens. Small specimens may contain bubbles or inclusions that appear doubled. Peridot may fill vesicular (tear-shaped) hollows and bubbles in volcanic lavas. It is the birthstone for August.

Occurrence Historically, some of the best specimens have come from St John’s Island off Egypt, from where it was mined for more than 3,500 years. Other localities include Australia, Brazil, China, Hawaii, Myanmar, Norway, Pakistan, South Africa and the USA.

QUARTZ
Quartz

Quartz is one of the most abundant minerals on Earth. It can be found worldwide as crystals in rocks and boulders, filling cracks or fissures in rocks, or in river and beach pebbles, sand or gravel. The name is from the Greek krustallos, meaning ‘ice’, because it was thought that colourless quartz was ice that had been turned into rock. Quartz is crystalline, made of crystals, but sometimes the crystals are so small they cannot be seen without the use of a microscope. If this is the case, the quartz is called microcrystalline or cryptocrystalline (from crypto, meaning ‘hidden’) – for example, chalcedony and agate. Transparent, crystalline quartz occurs in a wide range of colours (see the table below) and can be found as small delicate crystals as well as huge crystals as much as 7m (22ft) in circumference.

Occurrence Quartz occurs worldwide.

Colour of Crystalline Quartz

Name

Colourless

Rock crystal

Cream or white

Milky quartz

Pink

Rose quartz

Purple, violet or mauve

Amethyst

Yellow to brown

Citrine

Brown, brownish grey to black

Brown quartz, smoky quartz, Cairngorm (brown quartz and smoky quartz from the Cairngorm Mountains, Scotland) or Morion (dark brown to black opaque quartz)

AMETHYST

Quartz

The purple, pink, violet or mauve variety of crystalline quartz (amethyst) is often worn by bishops and other clergy, and has been said to guard against drunkenness. The name is from the Greek amethustos, meaning ‘sober’. The birthstone of February, amethyst can be found as record-breaking crystals in geodes so large you could stand inside them. These huge pockets form as gas bubbles from cooling lava flows get ‘frozen’ in. Later, silica-rich solutions fill voids and deposit crystals. Amethyst can be heat-treated to produce a colour change to yellow, which is then called citrine. Gemstones that are both purple (amethyst) and yellow (citrine) are called ametrine.

Occurrence Africa, Brazil, India and Sri Lanka are the main localities for gem-quality amethyst. The colour of the amethyst and type of inclusions can be used to indicate possible country of origin.

AVENTURINE QUARTZ

Quartz

Aventure quartz is mainly green with inclusions of a green mineral (fuchsite mica) which reflect the light. Inclusions of other minerals give the aventurine quartz a range of colours, including brown (pyrite inclusions), greenish brown (goethite inclusions), bluish green, bluish white and orange (pyrite inclusions). Gemstones may be polished or tumbled, or carved as small pieces for rings, brooches or necklaces. Copper inclusions in paste (man-made glass) have been used to imitate both aventurine quartz and aventurine feldspar. The copper inclusions in the simulant, which is called goldstone, may be seen using a magnifying glass or hand lens (×10 magnification) as bright triangles or hexagons.

Occurrence Aventurine quartz is found in Brazil, India and Russia. Other localities include Japan, Tanzania and the USA.

BROWN QUARTZ

Quartz

Brown quartz includes grey-brown (smoky quartz), brown-coloured quartz and black quartz (morion). Smoky quartz and brown-coloured quartz from the Cairngorm Mountains of Scotland may be called cairngorm. Colourless quartz (rock crystal) may be irradiated to give grey-brown or brown quartz. This suggests that brown quartz that has formed naturally may be coloured as a result of the natural radiation of aluminium-containing rocks. The change in colour caused by irradiation can be reversed using heat treatment to return the quartz to colourless quartz. Generally irradiated brown quartz has a stronger and more consistent colouring than quartz that has not been irradiated. As a result of the irradiation, there may be white colouring at the base of the crystal where it is attached to the rock.

Occurrence Although brown quartz is found worldwide, nowadays much of the brown quartz sold is irradiated colourless quartz. The Cairngorm Mountains of Scotland are famous for their dark-coloured quartz (cairngorm).

CAT’S-EYE QUARTZ (CHATOYANT QUARTZ)

Quartz

The cat’s-eye effect seen in some quartz when cut en cabochon is also called chatoyancy after the French word chat, meaning ‘cat’. The effect is due to fibrous inclusions in the gemstone and the reflection of light off the oriented inclusions such as crocidolite (asbestos) and hornblende. Cat’s-eye quartz may also have inclusions of the mineral hornblende. Cat’s-eye quartz may be pale yellow, golden yellow or brown. The colour may be enhanced or changed using dyes and stains, heat treatments or irradiation. The unnaturally bright blue, neon pink and orange-coloured cat’s-eyes, popular in jewellery and as loose polished gemstones, are often simulants that have been stained and dyed to imitate quartz cat’s-eyes.

Occurrence The main localities of cat’s-eye quartz are Brazil, India and Sri Lanka. Other localities include Australia and the USA.

HAWK’S-EYE (CHATOYANT QUARTZ)

Quartz

The cat’s-eye effect that can be seen in polished gemstones of hawk’s-eye is due to the fibrous nature of the mineral crocidolite (blue asbestos) and the reflection of light off inclusions within the gemstone. The arrangement of the fibres is not always straight; gentle curves, bends or sharp zig-zags add to the attractiveness and interest, giving individual character to polished gemstones. The blue-grey colour of the crocidolite is retained when crocidolite and quartz form as intergrowths. Hawk’s-eye occurs as slabs in rock and is often found with tiger’s-eye (see opposite). Hawk’s-eye may be a precursor to tiger’s-eye, changing to tiger’s-eye as further intergrowths are formed. Hawk’s-eye can be treated with acid to change the colour.

Occurrence The main locality for hawk’s-eye is Africa. Other localities include Australia, Brazil, India, Myanmar, Sri Lanka and the USA.

TIGER’S-EYE (CHATOYANT QUARTZ)

Chatoyant quartz

The cat’s-eye effect that can be seen in polished gemstones of tiger’s-eye is due to the fibrous nature of the mineral crocidolite (blue asbestos) and the reflection of light off in-clusions within the gemstone. In tiger’s-eye, the crocidolite fibres have been altered (mainly oxidised) to hydrous iron oxide, limonite, which gives it the golden yellow and brown colour. The fibrous nature gives the gemstone a striped appearance. As the gemstone moves, light causes pale-coloured stripes to appear darker and vice versa, adding to the interest of the gemstone. Heating can enhance the colour, producing deep red and brownish-red tiger’s-eye. Some hawk’s-eye (see p116) and tiger’s-eye has been acid-treated to produce what is marketed as grey tiger eye. Hydrochloric or oxalic acid has also been used to bleach tiger’s-eye to a light yellow colour.

Occurrence Tiger’s-eye is best known from Africa, where it often occurs with hawk’s-eye. Other localities include Australia, Brazil, India, Myanmar, Sri Lanka and the USA.

CITRINE

Quartz

The yellow or golden-yellow variety of crystalline quartz, citrine has been called lemon quartz or cognac quartz, or even Brazilian topaz. Citrine may be sold using these names – but beware; if it is not clearly stated that the gemstone is a citrine, it may cause confusion or even mislead. It should be remembered that citrine and topaz are different minerals with different physical and chemical properties and therefore different values, with topaz generally the more expensive of the two. Citrine is often found with amethyst, though amethyst is more common. Amethyst and smoky quartz can be heat-treated to give citrine, which may be why it is sometimes called burnt amethyst. Gemstones may be called ametrine when both amethyst and citrine can be seen in the same gemstone. Citrine is one of the birthstones for November.

Occurrence Most amethyst and citrine come from Africa or Brazil. Other localities include France, Russia and the USA.

MILKY QUARTZ

Quartz

Named after its cloudy white appearance, milky quartz is found in many igneous and metamorphic rocks. It is also found in sedimentary rocks, gravels and sands. When cut en cabochon or carved, its greasy or silky lustre may be confused with opal. The cloudy appearance is due to inclusions. The cloudiness and intensity of the milky white colour depends on the inclusions of gas and liquid bubbles:the more inclusions, the more cloudy the milky quartz. Milky quartz can be seen within other crystalline quartz. The most obvious are the phantoms seen within colourless rock crystal. Phantoms form during an interruption in crystal growth. The result may be a layer of inclusions, which appear to cover the surface of the crystal as they are enclosed by the continuation of crystal growth. The layer appears as a ghostly outline of a smaller crystal frozen within.

Occurrence Large crystals are found in Siberia. Other localities include Brazil, Germany, Madagascar, Namibia, the UK and the USA.

ROCK CRYSTAL

Quartz

Rock crystal is the clear colourless crystalline quartz. Rock crystal may be faceted, cut en cabochon or fashioned as beads, slices, geometric shapes (such as pyramids, obelisks, spheres, etc.) or small carvings, etc. Clusters of six-sided crystals are marketed as decorative pieces, and individual crystals are popular for their aesthetic and healing properties. Occasional large clear crystals have been polished as spheres, or crystal balls, used by fortune tellers and psychics. Thin slices of rock crystal have been used in watches and radios, as quartz vibrates at a constant rate once excited by, for example, a battery or electricity. Since 1950, when quartz was first made synthetically in the laboratory, it has been used in place of natural quartz in watches. It is also used in lenses and other precision instruments as well as having many more uses in industry.

Occurrence Rock crystal is found worldwide. The most important sources of rock crystal are in Brazil.

ROSE QUARTZ

Quartz

Rose quartz is a favourite because of its colour, from almost clear with a slight hint of pink, to pink and even red. Rose quartz is usually found as translucent to opaque masses without crystal shape (massive). Clear transparent crystals are rare. Transparent rose quartz that can be faceted is found in Brazil. The material is generally polished and carved as beads or decorative pieces such as figurines, or cut en cabochon. Rose quartz with inclusions of a fibrous mineral dumortierite may show a cat’s-eye effect (chatoyancy) or a star (asterism) when cut en cabochon. Usually, these effects are shown when a light is shone on the surface (reflected light). However, in rose quartz the effect is best shown when light is shone through the stone (transmitted light). Dyes and stains have been used to intensify the colour of a very pale rose quartz.

Occurrence Most rose quartz is from Brazil or Madagascar. Other localities include Afghanistan, Canada, Germany, India, Russia and the USA.

RUTILATED QUARTZ (SAGENITE)

Quartz

Rutilated quartz is colourless quartz (rock crystal) with inclusions of long, needle-like crystals of rutile. The rutile inclusions may be red, black or brassy yellow and have a metallic lustre. The crystals may be so fine that they have the appearance of wisps of golden blonde hair, which explains why rutilated quartz is also known as Venus-hair stone. Another name is sagenite, but this should only be used to refer to rutilated quartz where the inclusions have been identified as rutile and the crystals are not random, but are arranged in radiating interpenetrating, sometimes star-like, patterns, with constant angles between crystals of 65°35' and 55°44'.

Occurrence Rutilated quartz is best known from Brazil. Other localities include India, Madagascar, Switzerland and the USA.

TOURMALINATED QUARTZ

Quartz

Tourmalinated quartz is colourless quartz (rock crystal) with inclusions of long, often needle-like, crystals of the mineral tourmaline. Tourmaline crystals have a distinctive triangular cross-section;the triangle is not a straight-sided triangle, but a convex triangle with sides that bulge outwards. Tourmaline crystals found within quartz are usually of the opaque black variety called schorl, but may also be dark green (elbaite), dark brown or golden in colour and very rarely blue (indicolite). The inclusions appear to be arranged haphazardly rather than being aligned, which gives each crystal a unique appearance. Tourmalinated quartz is usually tumbled or polished as beads or small irregular-shaped pieces, which are usually set in silver and fashioned as pendants, necklaces, bracelets, rings and brooches.

Occurrence Polished spheres made from Brazilian material may be several inches across. Other localities include India, Madagascar, Switzerland and the USA.

RHODOCHROSITE

Rhodochrosite

Rhodochrosite is named after the Greek words rhodon meaning ‘rose’and chroma meaning ‘colour’, after the pink to red colour caused by manganese. Rhodochrosite rarely occurs as transparent crystals large enough to facet. Although good-quality gemstones have been found in, for example, Colorado (USA), and have been cut for collectors, they do not make good hard-wearing gemstones, as they are brittle and relatively soft (hardness 4 on Mohs’ scale). More often, rhodochrosite occurs as banded rocks or stalactites, which, when cut and polished, show a concentric pattern of light and dark pink, red or white uneven circles. Rhodochrosite has also been known as Inca rose, named after the Incas who worked the silver mines of Argentina.

Occurrence Rhodochrosite has been mined in Argentina since the 13th century. The main producer is now the USA. Other localities include Brazil, Canada, Mexico, Peru and South Africa.

RHODONITE

Rhodonite

Rhodonite should not to be confused with rhodochrosite (similar colour) or rhodolite garnet (similar spelling), whose names are derived from the Greek rhodon/rhodos meaning ‘rose’, which refers to their similar rose colour. Rhodonite very rarely occurs as crystals, and is usually found as opaque or translucent massive (without crystal shape) specimens with black veins or patches caused by manganese oxide. The presence of black patches should distinguish it from rhodochrosite at a glance. Where black patches are absent, further tests may be needed to distinguish the two minerals. Rhodonite is harder-wearing than rhodochrosite and more suitable as a gemstone. Massive material is usually cut en cabochon, polished as beads, used in cameos or made into small carvings. Large slabs can be used as decorative panels (facades) on walls.

Occurrence The main localities are Australia and Russia. Other localities include Brazil, Canada, Mexico, New Zealand and the USA.

SPINEL

Spinel

Spinel occurs in a range of colours including pale violet, pink, blue, mauve, grey-blue, blue and black, but the red spinel is the best known. Both red spinel (also known as balas ruby) and ruby are coloured by chromium, and it is this similarity, as well as a similar hardness, lustre and density, that has led to confusion. The famous gemstone called the Black Prince’s Ruby in the Imperial State Crown of the British Crown Jewels is, in fact, a spinel (there is a small ruby embedded in the spinel). Spinel is found in igneous rocks and in river gravels. Synthetic spinel has been manufactured in the laboratory since 1910 and has been used to imitate gemstones, including ruby and diamond.

Occurrence Main localities are India, Madagascar, Myanmar and Sri Lanka. Other localities include Afghanistan, Australia, Brazil, Pakistan, Russia and the USA.

TAAFFEITE (MAGNESIOTAAFFEITE)

Taaffeite (magnesiotaaffeite)

Taaffeite is a very rare gemstone, which ranges in colour from near-colourless to pink, red, mauve, brownish-purple, blue, greenish and violet. The gemstone is famous for being the first to be identified as a new mineral having already been faceted as a gemstone. Taaffeite is named after Count Taaffeite (1898–1967), who found the gemstone in a jeweller’s shop in Dublin in 1945. It was initially thought to be a mauve spinel, but, on further testing, was found to be a new mineral. The results were published in Mineralogical Magazine in 1951 in a paper by several mineralogists and gemmologists from the Natural History Museum and The Gemmological Association and Gem Testing Laboratory of Great Britain.

Occurrence Taaffeite has been found in gem gravels in Sri Lanka, and in China and Tanzania, but not in the rock in which it was formed.

TOPAZ
Topaz

Topaz occurs in a range of colours including colourless, pink, brown, golden-yellow (sherry topaz), grey-green, green and blue. It is found in igneous rocks, including pegmatites, granites and volcanic lavas. Water-worn pebbles found in alluvial deposits may have a surface like frosted glass. Topaz has a hardness of 8 on the Mohs’ scale, a greasy feel and adamantine lustre. Care should be taken not to damage topaz crystals and cut gemstones, as they may break along one direction of perfect cleavage (leaving a completely flat surface). Colourless or pale brown topaz may be irradiated and heat-treated to give bright blue gemstones. Yellow topaz can be heat-treated to give the rarer pink topaz. Topaz is one of the birthstones for November.

Occurrence Brazil, Myanmar, Sri Lanka and the USA. Pink topaz is found in Brazil, Pakistan and Russia.

A selection of topaz cut stones

TOURMALINE
Tourmaline

Tourmaline has a wider range of colours than any other gemstone. The addition of small amounts of trace elements such as iron, manganese, chromium, vanadium, titanium and copper to the already complex chemical composition causes the different colours. The mineralogy of the tourmaline group is complex;members of the tourmaline group with the same colour may have a different chemical composition, but gemstones are usually named by their colour rather than their mineralogy. Schorl, the black tourmaline, is the most common tourmaline. Most transparent coloured tourmaline used as gemstones is from the elbaite subgroup, named after the Italian island of Elba. Within a single crystal, tourmaline may show many colours (parti-coloured). The colour or intensity of colour may also vary when viewed from different directions (pleochroism). The best colour is usually seen when viewed along the long axis of a crystal (as if looking straight into the point of the crystal). Care must be taken by the lapidary, so that the best colour is seen when the gemstone is viewed through the front of the stone. Pink tourmaline is one of the birthstones for October. To show the colour to its best advantage, tourmaline may be cut at round brilliants, rectangular cuts or carved. Star stones are cut en cabochon (as cabochons).

Occurrence The main tourmaline localities are Africa (Kenya, Mozambique, Namibia and Tanzania) and Brazil. Other localities include Afghanistan, Madagascar, Pakistan, Sri Lanka and the USA.

ACHROITE (ELBAITE)

Tourmaline

Achroite is the transparent to translucent colourless tourmaline, a variety of elbaite. It is named from the Greek word achroos, meaning ‘without colour’, or ‘colourless’. As it is colourless, it does not show the pleochroism seen in coloured tourmaline and can therefore be cut and set in jewellery in any direction. Fibrous achroite may be faceted or cut en cabochon. Pink tourmaline can be heat-treated to remove its colour, giving the rarer achroite.

Occurrence The main locality is in southwest England. Other localities include Afghanistan, Madagascar and the USA.

INDICOLITE/INDIGOLITE (ELBAITE)

Tourmaline

Dark blue tourmaline is called indicolite or indigolite by gemmologists. Blue tourmaline is usually elbaite tourmaline. Where the colour is considered too dark, it may be heat-treated to lighten the colour. Bright neon-blue tourmaline from Paraiba (Brazil) is called paraiba tourmaline (see opposite). Lilac to violet-blue tourmaline, first found in Russia, is called siberite (see p136). In Russia, indicolite tourmaline is found in granites and the clays formed from weathered granite. Crystals may be pencil-thin, striations (ribs or grooves in the surface) are obvious and the cross-section shows a triangle with a curved outline (bulging outwards).

Occurrence Localities include Brazil (blue-green), Madagascar (blue), Pakistan, Russia and the USA.

PARAIBA (ELBAITE)

Tourmaline

Following years of exploration by Heitor Dimas Barbosa at the Mina da Batalha (the Batalha Mines), near the village of São José de Batalha (Brazil), paraiba tourmaline was found in 1989. Following the find, there was a rush to discover more, and an area of about 80,000sq m was virtually levelled as a result of the number of tunnels dug by enthusiastic miners and gem collectors. The tourmaline is named after Paraiba, the state in Brazil where it was discovered. Paraiba tourmaline is sought-after because of its distinctive colour and rarity. Sometimes described as neon blue, the vivid turquoise blue to blue-green is due to copper, sometimes with additional manganese.

Occurrence The Batalha Mines of Paraiba, Brazil, are the only locality for paraiba tourmaline. Tourmaline from Mozambique and Nigeria, which has a similar colour, has been sold as paraiba tourmaline.

SIBERITE (ELBAITE)

Tourmaline

Siberite is named after the violet to violet-blue coloured tourmaline which was first found in Siberia, Russia. Crystals are usually opaque. Siberite is in the elbaite group and is a type of indicolite tourmaline. Siberite crystals have a curved triangular cross-section (bulging out) and vertical striations along the length of the crystal.

Occurrence Localities include Brazil, Namibia, Pakistan and Russia.

RUBELLITE (ELBAITE)

Tourmaline

Pink and red tourmaline is called rubellite after the Latin word for red. Rubellite is usually, though not always, elbaite tourmaline, which includes most of the colours of the rainbow. Rubellite was a favourite of the last Empress of China, Ts’u Hsi. She is said to have bought a tonne of rubellite from the Himalaya Mine in California (USA) and to have had a pillow made of rubellite. Crystals are striated and have a curved triangular cross-section which bulges out. The darker red rubellite is similar to the colour of spinel or ruby, and is sought-after for its rarity. The bright pinks are popular for their colour. Fibrous rubellite may be cut en cabochon to show the cat’s-eye effect.

Occurrence Localities include Afghanistan, Brazil, Canada, East Africa (particularly Nigeria), Madagascar, Myanmar, Russia and the USA.

GREEN TOURMALINE (ELBAITE)

Tourmaline

The colour of this tourmaline varies from a dark brownish-green, through green, to bright emerald green. An emerald green-coloured tourmaline, sometimes sold as chrome tourmaline, is coloured by chrome. Chromdravite tourmaline may have a bright emerald green colour and is in the chromdravite mineral group rather than elbaite tourmaline. Emerald green tourmaline from Tanzania is sold as chrome tourmaline.

Occurrence Localities for green tourmaline include Brazil, Kenya, Madagascar, Namibia, Nigeria, Sweden, Tanzania and the UK. Emerald green-coloured tourmaline is found in Brazil, Namibia, Nigeria and Tanzania.

YELLOW TOURMALINE (ELBAITE)

Tourmaline

A greenish-yellow or yellow coloured elbaite tourmaline, the crystals may be transparent or translucent. Fibrous yellow tourmaline from, for example, Sri Lanka or China, may be faceted or cut en cabochon. Yellow tourmaline usually has a brownish-yellow colour. In 1990 a bright yellow tourmaline was discovered in Malawi, East Africa. The gemstones, coloured by magnesium, have been described as electric yellow and have been sold as canary tourmaline, named after the bright yellow feathers of the canary bird. Heat treatment can remove traces of brown and enhance the colour of yellow tourmaline. Golden yellow and greenish yellow tourmaline from Madagascar have been sold as yellow tourmaline (tsilaizite), and yellow tourmaline from Thailand has been sold as lemon tourmaline.

Occurrence Localities for yellow tourmaline include China, Madagascar, Sri Lanka, Thailand and Malawi, the source of bright yellow ‘canary tourmaline’.

PARTI-COLOURED TOURMALINE (ELBAITE)

Tourmaline

Tourmaline has a complex chemical composition, and small amounts of trace elements such as iron, manganese, chromium, vanadium, titanium and copper affect the colour. This complexity allows for a single crystal of tourmaline to show more than one colour. These parti-coloured tourmalines may show a colour and colourless parts or may have as many as twelve or so different colours. Parti-coloured tourmalines may be faceted, polished or carved to show two colours (bi-coloured), three colours (tri-coloured) or a range of colours. An orange and pink bi-coloured tourmaline from Sri Lanka has been described as having padparadscha colour. Care should be taken not to confuse this with the pinkish-orange corundum called padparadscha. Tri-coloured tourmaline – for example, green, pink and orange – is found in Brazil.

Occurrence Parti-coloured tourmaline localities include Argentina, Brazil, Pakistan, Sri Lanka and the USA.

WATERMELON TOURMALINE (ELBAITE)

Tourmaline

Watermelon tourmaline is bi-coloured. The tourmaline is mainly of the elbaite and liddicoatite tourmaline groups. The crystals are colour zoned and have a pink core surrounded by a green rim. When cut to show the cross-section, the colours are those of watermelon, with the pink fruit and green skin. Polished cross-sections are used in necklaces, brooches and pendants. Watermelon tourmaline may also be polished as irregular pebbles, or carved as small figurines or animal carvings.

Occurrence Localities include Argentina, Brazil, Pakistan, Sri Lanka and the USA.

DRAVITE

Tourmaline

This tourmaline is named after the Drave, the Latin for the River Drau in Slovenia. Dravite includes light to dark brown, to brownish-black and dark-yellow translucent to opaque crystals with the characteristic convex (bulging out) triangular cross-section. Crystals are heavily striated (ribbed) along their length. Double-ended (doubly terminated) crystals are hemimorphic, which means that the ends are different shapes. Dravite is the magnesium-rich tourmaline. Heat treatment can be used to lighten the colour of dark brown dravite. Brown dravite tourmaline may be marketed with names that describe their colour, such as light cognac tourmaline, golden cognac and sherry tourmaline.

Occurrence Gem-quality dravite is found in Brazil. Other localities include Africa, Australia, Canada, Russia, Sri Lanka and the USA.

SCHORL

Tourmaline

Schorl, the black tourmaline, is the most common of the group. Its colour is due to the presence of iron. Crystals are opaque and have the distinctive triangular cross-section, where the triangle has convex sides (bulging out) rather than straight sides. There are strong striations along the length of the crystals. Crystals range from very fine needle-like crystals only millimetres long, to record-breaking crystals many metres long. The name is from an Old German mining term. Tourmalinated quartz, colourless quartz (rock crystal – see p123) with inclusions of tourmaline, is fashioned as a gemstone.

Occurrence Schorl is found worldwide. Main localities include Australia, Brazil, Canada, Madagascar, Pakistan and the USA.

TURQUOISE

Turquoise

The sky-blue turquoise of Iran (formerly Persia) has been mined for more than 3,000 years and may have been mined in Egypt even earlier. Also known as Persian blue, turquoise is named after Turkey, from where the Persian material was introduced to Europe. The colour is due to the proportions of iron and copper;generally, the more copper, the brighter the blue and the less green. The surface is porous and may dry out, becoming dull or cracked. Polishing or impregnating the gemstone with oils, wax or resin offers protection and enhances its colour. Spiderweb turquoise has black veins of brown geothite or black manganese oxide. Since 1972, imitation Gilson turquoise has been used in the same way as natural turquoise – for example, cut and polished as beads or small spheres, or used in inlays and mosaics. Turquoise is one of the birthstones for December.

Occurrence Localities include Australia, Chile, Iran, Mexico, Russia, Turkestan and the USA.

ZIRCON

Zircon

The adamantine (diamond-like) lustre, hardness and wide range of colours (including colourless, green, yellow, orange, brown and blue) make zircon a popular gemstone. Zircon has been mined in Sri Lanka for use as a gemstone for more than 2,000 years. It is brittle and care should be taken not to chip gemstones set in jewellery. Colourless zircon has been mistaken for diamond. Zircon should not be confused with cubic zirconia, an artificial stone that can be made in many colours to imitate a variety of gemstones. Natural blue zircon does occur, though much of the blue zircon that is sold is brown zircon from Thailand, Cambodia, Sri Lanka and Vietnam that has been heat-treated to produce a range of blues, from pale to vivid neon. Zircon is one of the birthstones for December.

Occurrence Localities include Australia, Brazil, Cambodia, Myanmar, Nigeria, Russia, Sri Lanka, Tanzania, Thailand, the USA and Vietnam.

ZOISITE
Zoisite

Zoisite is named after Baron von Zois, who discovered the gemstone in the Austrian Alps. Transparent, gem-quality zoisite occurs in a range of colours, including yellow, green, brown and the blue variety called tanzanite (see opposite). An opaque pink massive variety, called thulite, is usually cut en cabochon or polished as a decorative gemstone. Thulite, from Norway, is coloured by manganese. It usually occurs intergrown with white quartz, which may give an attractive pattern to the surface of the polished piece. Massive green zoisite, which contains ruby, can be polished as thin slabs, carved, polished as spheres or tumbled as irregular shapes. Zoisite is strongly pleochroic. It may be heat-treated to enhance its colour.

Occurrence Localities include Australia, Austria, Kenya, Norway, Pakistan, South Africa, Sweden, Tanzania, the USA and Zimbabwe.

TANZANITE

Zoisite

Tanzanite is the blue zoisite. Named after Tanzania, where it was discovered in 1967, the trade name was introduced by the jewellers Tiffany & Co. It is usually heat-treated to enhance the colour, as most tanzanite is a dull green or brown colour when mined. Tanzanite is strongly pleochroic and gemstones may show three different colours (trichroic) – red, purple and blue – when viewed from different directions. The lapidary must take care to cut and set the gemstone so that its best colour is shown when it is viewed through the front. In October 2002, the American Gem Trade Association (AGTA) announced that tanzanite had joined zircon and turquoise in the traditional list of birthstones for the month of December.

Occurrence Tanzanite is only found at Merelani, near the town of Arusha, ten miles south of the Kilimanjaro International Airport in northern Tanzania.

ORGANIC GEMSTONES

The gemstones in this part are all organic. They are derived from plants and animals. The organic material is from living animals and plants – for example, pearl, shell or bone, or from the remains of dead plants or animals. Even fossils can be used as gemstones;for example, amber is a fossil tree resin, and jet is a fossil coal formed from the buried remains of ancient trees, some of which are now extinct.

The gemstones here are mainly those that are polished or carved rather than faceted for use in jewellery. They are generally opaque or translucent (light can be seen through them, but they are not completely transparent) and most are not as hardwearing as the mineral (inorganic) gemstones.

AMBER
Amber

Amber in jewellery is best known as golden or yellow polished or faceted beads that have a warm glow and may include insects, plants or bubbles of air. Each piece may be clear or cloudy and will have its own character, colour and inclusions. Colours range from pale yellow to deep golden brown, green and blue.

Amber is named depending on its occurrence (for example, simetite from the Mediterranean) or its appearance (for example, red amber, blue amber, green amber and yellow amber, black amber and cognac amber). White amber, sometimes called bone amber, or cloudy amber, has numerous inclusions or air bubbles that give the cloudy appearance. Heating in oil may clear cloudy amber. The most sought-after amber is clear and transparent and has a bright yellow to golden colour.

Amber is a fossilised tree resin. It floats on salt water and irregular-shaped pieces of Baltic amber, released from on-land deposits or washed from under-sea layers, can be found as far away as Norway, Denmark and the east coast of England.

Occurrence Amber from the Baltic region is the best known. Other localities include Canada, the Dominican Republic, France, Germany, Italy, Mexico, Myanmar, Romania, Sicily, Southeast Asia, Spain and the USA.

Amber named after locality

Locality

Succinite

Baltic region, including Poland, Russia, Latvia, Lithuania, Estonia and the Baltic Sea

Simetite

Sicily and the Mediterranean off Sicily

Burmite

Myanmar (formerly Burma)

Rumanite

Romania

Chiapas amber

Mayan mines in Chiapas, Mexico

Malaysian amber

Sarawak amber from Malaysia, specifically the island of Borneo

AMBROID

Amber

Although large pebbles of amber have been found, it generally forms as thin layers or nodules. Often, these small pieces are not large enough to be polished or faceted as beads for a necklace or bracelet, or set in a ring, pendant or earrings.

In order to make the most of these small pieces plus any scraps left over as a result of fashioning larger pieces, they may be heated and pressed together to make a larger piece. This is called ambroid. The process may cause the flattening and elongation of bubbles and inclusions, which may be used to identify ambroid. Heat treatment may cause internal cracks. Light reflecting off these results in a bright-coloured reflection or spangle, which gives it the name sun-spangled amber.

Amber is an organic material. Care should be taken not to wear it in hot sunshine or very hot water, as it may lead to drying out and cracking. Weathered amber may have a translucent pitted skin and the colour may mature to a darker golden brown.

COPAL

Amber

Resin is a sticky substance, produced by some trees to protect against wood-boring insects, which acts as an antiseptic covering wounds in the bark. Copal is a modern resin and amber is a fossil resin. Although most resin can be clearly defined as either copal or amber, there are some ‘older’copals and ‘younger’ ambers, where the distinction between the two is not so clear. Scientists continue to debate the use of the terms with the aim of defining the ‘cut off’ between the two more clearly.

The colour of amber is partly due to the source of the resin and the species of tree that produced it. Pale yellow to yellow amber is thought to be mainly associated with pine trees, and darker golden-brown amber is produced by deciduous trees.

Modern tree resins – for example, Kauri gum (copal) from New Zealand – have been used to imitate amber. Amber imitations may also be made of glass (paste), plastics and man-made resins (synthetic resins). Be aware:finding insects in a bead of so-called amber does not prove it is amber;they may have been added to imitations or modern tree resins to mislead.

Occurrence Localities include Africa (e.g. Kenya, Nigeria and Tanzania), Australia, Indonesia, Japan, New Zealand (Kauri gum) and South America (e.g. Brazil and Colombia).

CORAL
Coral

Coral is a living rock;the structure is made up of both the skeletal remains of marine animals called coral polyps and living organisms related to the sea anemone. Corals may consist of individual organisms, which grow as conical or horn-shaped masses, or they may form part of a colony. As the polyps develop, they lay down a mineral skeleton, which on death forms branch-like structures with a distinctive striped or wood-grain surface pattern, adding to the size of the coral. In this way, coral reefs can be built up over time. The most famous is the Great Barrier Reef off Australia.

Most corals are red, pink or white, have skeletons made of calcium carbonate and are generally associated with warm water. Black and golden coral is made of conchiolin – a tough, horn-like material. Red and pink coral have been harvested for thousands of years. The Romans gave coral to children to protect them from harm.

Following increased awareness of the importance of maintaining a healthy environment for coral growth, and as a result of the loss of vast areas of coral following pollution and changes in water temperature and water depth, coral harvesting has become more strictly regulated.

More than half of all the coral harvested is processed in Torre del Greco, Italy. Dull coral is polished to give a bright vitreous lustre and the wood-grain pattern incorporated in designs. Coral is usually cut en cabochon, though spherical beads and small slices for inlay work are also popular.

Occurrence Localities for red, white and pink coral include the Mediterranean, and coasts of Africa, Egypt (Red Sea), Hawaii, Indonesia, Japan and Malaysia. Black and golden coral localities include the coasts of the West Indies, Australia and the Pacific Islands.

JET
Jet

The jet black of this organic material is as a result of its carbon content. Jet is formed from the remains of wood, buried, compacted and altered over time to give a hard, black or dark brown coal that can be faceted or polished for use as a gemstone. The wood, which grew in Jurassic forests 180 million years ago, is related to the modern monkey puzzle tree. Light in weight and with a hardness of only 2½ on Mohs’ scale, jet takes a good polish and is easy to work with. Jet has been mined for more than 3,000 years. Worked pieces have been found in prehistoric burial sites, and, during the Roman occupation of England, it was exported to Rome.

Following the death of Prince Albert in 1861, his wife, Queen Victoria, chose to wear black to show she was officially in mourning – a state she maintained for the rest of her life (another 40 years). Dark and sombre jewellery was customary during periods of mourning, and jet soon became the standard gemstone of mourning. It has also been worn by the clergy, fashioned as rosary beads or crucifixes.

Occurrence Whitby, near Scarborough on the coast of Yorkshire (England), is the best-known locality for jet. Other localities include China, France, Germany, India, Poland, Portugal, Russia, Spain, Turkey and the USA.

PEARL
Pearl

Pearls form in shellfish called molluscs (i.e. oysters, mussels, clams, scallops and snails). The mollusc is a soft-bodied animal with a hard outer shell. Natural pearls (see pp160–161) form within the mollusc as a mechanism to reduce the irritation caused by the presence of grit, food or some other irritant. They produce layers of aragonite and conchiolin, the same materials that form the shell, and cover the irritant with a pearl. These alternating layers produce nacre, the mother-of-pearl that gives pearls their glossy iridescent surface.

For thousands of years, pearls have been collected by diving in the oceans of the world (for example, from the pearl beds of the Indian Ocean or the Pacific) or from freshwater rivers. The depths at which marine pearls are found, and the fact that the waters may be shark infested, make their retrieval dangerous, even with modern diving equipment. River pearls are easier to harvest;they are generally irregular in shape (baroque).

There are about 100,000 species of mollusc and each is capable of forming a pearl, but without human intervention this rarely happens. It has been estimated that only 1 in 10,000 pearl oysters will contain a pearl. The range of processes available and the variety of species that are particularly suitable for pearl production for the jewellery trade result in a vast array of pearls with different colours (including white, pink, purple, gold and black), shapes (from perfect spheres to irregularly shaped baroque pearls) and sizes.

The shape and size depends on the species of the mollusc, the method (for example, the size of the nucleus), where in the mollusc the pearl formed, the length of time allowed for the production, water temperature and composition, and the health of the mollusc. The healthier the mollusc and the longer the time allowed, generally the larger the pearl. Spherical pearls are produced using a large, perfectly spherical nucleus.

Pearls are described depending on how and where they have been produced – naturally or cultured and in marine (saltwater) oceans or artificial ponds, in freshwater lakes, rivers and streams or on land. Cultured pearls (see pp162–166) are categorised depending on whether they are nucleated (contain a nucleus) or not (non-nucleated).

Imitations include glass or plastic beads covered in a mixture of fish scales and varnish. Ammolite is a fossil ammonite (extinct shellfish) that has an iridescent shell of nacre. Pearl is the birthstone for June.

NATURAL PEARLS

Most natural pearls are marine pearls, formed in molluscs that live in the salt water of the oceans and seas. They have a smooth, lustrous surface. They are normally white or a silvery-grey, but may also be pink or black. The colour of the pearl depends mainly on the type of mollusc, while the size depends on the mollusc and the length of time that the pearl has been forming before being harvested. These include the categories on the opposite page.

Marine pearls
Divers have harvested pearls from the pearl beds of the Persian Gulf, Red Sea and Gulf of Mannar (off the coast of Sri Lanka) in the Indian Ocean for thousands of years. The Pacific Ocean, particularly around the Philippines, Polynesia and Australia, also has a long record of pearl harvesting. Abalone (USA) and Conch shells (Caribbean, particularly Bahamas) have been known to produce pearls, but they are very rare. Marine pearls, as with other pearls, are fairly soft and can be scratched easily. Spraying perfume near pearl jewellery should be avoided as the pearls may become discoloured or etched.

River pearls

Pearl rushes, similar to the famous gold rushes of the 19th century, were sparked by discoveries of river pearls in the Mississippi River basin in the USA. Mississippi pearls were popular in the Art Nouveau jewellery of the 1920s, but river pearls are now very rarely found. In the 19th century, pearl fishing was also carried out in the rivers of northern Europe (including Scotland, France, Germany and Austria), Scandinavia (including Norway and Sweden) and Russia. Scottish river pearls are still collected.

Seed pearls

Seed pearls are very small natural pearls with a diameter of less than 2 mm (0.1in).

CULTURED PEARLS

Cultured pearls have been produced commercially since the early 20th century. The vast majority of pearls on the market are cultured pearls from the pearl farms of Japan, China, Australia and Polynesia (including the South Sea and Tahitian pearls). Cultured pearls may be dyed, bleached, polished (buffed), coated (for example with plastics) or irradiated to improve their appearance.

Cultured pearl production

Various techniques have been used to produce cultured pearls. The mollusc uses the same process as it would naturally (see p158), but in a cultured pearl the irritant is introduced artificially. A nucleated cultured pearl will also have a nucleus inserted.

A healthy pearl oyster is collected from open waters or from large enclosures where they have been bred (farmed) by pearl farmers.

The oyster is wedged open.

A piece of soft tissue (mantle) from another oyster and a glass or plastic bead (nucleus) is inserted in the soft tissue of the gonad (reproductive organ). The inserted mantle will become the pearl sack, which secretes the layers of mother-of-pearl (nacre) around the nucleus to form the pearl. Several beads may be inserted in a single oyster.

The wedge is removed, and the oyster is placed in a tray or basket and lowered into water suspended from a bamboo raft (in a pen, pool, pond, estuary or lagoon, etc. near shore) where, for a couple of weeks, it recovers and begins to coat the nucleus with nacre.

Oysters that do not recover are removed. The remainder are transferred into trays and moved to larger pens or open water further offshore, where they hang from racks at depths of 10–15m (30–50ft). They are left to grow for between six months and three years depending on the species of the mollusc, how fast the pearl is growing and what size of pearl is needed. They may need regular feeding, cleaning and health checks.

When the oysters are ready, they are harvested. The oyster is opened and the pearl removed. Soft tissue may be taken to be transplanted in another oyster to repeat the process. Removal of the pearl usually kills the oyster, but some of the larger species of mollusc may survive. Surviving oysters may be reused to produce more cultured pearls.

Mabe pearls are cultured by gluing a half-bead nucleus against the inside of the shell. Blister pearls grow attached to the inside of the shell instead of growing in the mantle;where they are joined to the shell, no nacre is developed.

Akoya pearls

Pearls more than 7 mm (¼ in) in diameter from the akoya oyster are generally from Japan, while smaller ones are more likely to be from China, Hong Kong, Korea or Sri Lanka. They are fairly spherical and range in colour from white, pink and yellow, to green, grey and blue-grey.

Keshi pearls are tiny pearls that form as a larger cultured pearl is forming in an akoya oyster. They have not been cultured; they just appear. They have the same colours as akoya pearls, but do not have a nucleus and form as natural pearls within the oyster. Keshi pearls are generally irregular in shape (baroque).

South Sea and Tahitian pearls

Cultured in the large mollusc Pinctada maxima, South Sea pearls are the largest cultured pearls. They have similar colours to the akoya pearls;the white-rose and the gold-coloured pearls are particularly popular.

Keshi pearls with a diameter of more than 10 mm (⅓ in) can appear during the culture of South Sea and Tahitian pearls. They are irregular in shape (baroque), have no nucleus and may be termed natural;they are referred to as Tahitian or South Sea keshi pearls.

The only natural black pearls are those from the mollusc Pinctada margaritifera. Pearls may be dyed or soaked in silver nitrate to appear black.

Biwa pearls

The first freshwater cultivated pearls were produced in Japan’s largest freshwater lake, Lake Biwa near Kyoto, and sold commercially in the 1930s. Japanese biwa pearls occur as irregular pearls without a nucleus (the mollusc would not accept a nucleus). Production was interrupted by World War II. By the 1950s, freshwater pearls were sold in Japan as a less expensive and more colourful alternative to the marine material. Biwa became associated with freshwater pearls and, until recently, all freshwater pearls were sold as biwa, regardless of their origin.

Following pollution of the lake, Japanese biwa pearl production diminished, only to be replaced and surpassed in 1968 by freshwater biwa pearls from China, where production costs were low and technology and expertise was advancing. The early material was nicknamed ‘rice crispie’ pearls because of their shape. Nowadays, biwa pearls from China are produced in a vast range of colours (including cream-white to salmon-pink, salmon-orange, peach, wine-red and violet, plus the more exotic peacock, copper, silver and black coloured pearls), shapes (including rice, potato, stick and square) and sizes. Chinese biwa pearls may have a nucleus.

Rice pearls

The shape of rice pearls (like wrinkled grains of rice) is due to the speed of cultivation, resulting in irregular thickness of the nacre and occasional pitting of the surface. Rice pearls are produced in fresh water – for example, in China. Other names used to sell irregular of fancy-shaped pearls include potato pearls, corn pearls, chiclets (square-shaped), lavender button pearls, plus copper, pink or peacock biwa stick pearls (with stick-shaped pearls as long as 7.6 cm (about 3in).

IVORY
Ivory

Teeth and tusks of animals such as elephant, walrus, narwhal, hippopotamus, sperm whale, orca (whale), warthog, wild boar and the extinct mammoth are made of ivory. Tusks are large teeth that have evolved so that they stick out past the lips. The main component of ivory is dentine, which forms the main bulk of the tooth or tusk.

Originally, the term ivory referred only to elephant tusks, but the chemical structure of teeth and tusks of mammals is the same and the term is now used for any mammal teeth or tusks that are large enough to be carved or engraved.

Mammoth tusk ivory carved more than 30,000 years ago has been found in caves in France. Ivory has been used to make piano keys, billiard balls, hair combs, chess pieces, inlay, small carved objects including netsukes (small Japanese sculptures) and jewellery.

Occurrence Historically, African elephant ivory has been the major producer of ivory;Indian elephant ivory is softer and yellows more easily. Other ivory producers include Europe, Indonesia and Myanmar.

IVORY AND TRADE

An estimated 700,000 elephants were slaughtered in the ten years prior to 1989, when a worldwide ban was introduced to protect populations of ivory-producing animals – particularly elephants. In 2002 the United Nations partially lifted the ban on ivory trade, allowing a few countries to export certain amounts of ivory.

Since then, bans and trading restrictions have been lifted or reintroduced intermittently as required in order to protect elephant populations while also allowing legal trade. Trade in antique mammoth ivory is not illegal.

Modern ivory substitutes include vegetable ivory (part of the ivory nut palm), plastic, jasper, horn and bone.

SHELL
Shell

Made of calcium carbonate, shells show a wide range of sizes and colours, from the iridescent colours of pearl oyster shells (Pinctada maxima and Pinctada margaritifera), blue-green iridescence of abalone, paua (the type of abalone that is found in the waters around New Zealand) and topshells (trochidae), to the delicate white and pink layers of the conch shell.

In addition to marine shells, a wide range of river and terrestrial shells is also used as beads and in jewellery, particularly if they show a colourful iridescence.

Occurrence Shells are found worldwide. Conch is found in the Bahamas (where conch fritters are a favourite food), Madagascar and the Maldive Islands. Abalone molluscs are found off the coast of South Africa and the USA. Maori people have a long tradition of gathering paua for its meat, as well as using the shell in their carvings and as a Taonga(the Maori word for treasure). Paua has become the shell associated with gifts from New Zealand.

Mother-of-pearl

cabochons, mosaic pieces for inlay, or as decorative pieces.

Some shells have an iridescent coating of mother-of-pearl. Mother-of-pearl is made of nacre, the same material that coats a pearl. Nacre is usually a pale colour, though the nacre lining the shells of Tahiti can be dark. Where the layer is thick enough, mother-of-pearl can be fashioned as beads, spheres or domed cabochons, but mostly thin layers are used, for example, as low Shells that have layers of different colours may be fashioned as cameos. The outer layer is cut away to reveal an inner layer of a different colour. Examples include the pink and white of the conch, and the spider conch (Lambis lambis), the mottled cream and brown of the tiger cowrie (Cipraea tigres) with the violet inner layer, and the white outer layer of shells (including Cassidae madagascarensii), which have an inner layer of beige or brown.

Cameos

Tortoiseshell

Tortoiseshell was made by warming and flattening the shell of the Hawksbill turtle and was used to produce, for example, tortoiseshell cases, hair combs and brooches. However, since 1973 this turtle has been an endangered species and the sale of tortoiseshell has been banned.

GEMSTONE REFERENCE

The tables in this section provide a quick and easy reference guide giving further information about the gemstones listed in this book. They cover:

gemstone name

chemical formula

crystal system

hardness

Specific Gravity (SG)

Refractive Index (RI)

Birefringence (DR)

lustre.

CRYSTAL SYSTEM

Gemstones are divided into crystal systems, which are a means of classifying them by their crystal shape and symmetry. There are seven crystal systems:

cubic

tetragonal

hexagonal/trigonal

orthorhombic

monoclinic, and

triclinic.

Axes of symmetry

HARDNESS

The hardness of a gemstone is given as a number on Mohs’ scale of hardness. The scale goes from 1 (talc), the softest, to 10 (diamond), the hardest-known natural material. The scale is a comparative scale, based on 10 of the most common minerals. Friedrich Mohs tested each by seeing whether it would be scratched or scratch others in the group. By testing each, he was able to put them in order of ‘scratchability’. A gemstone will scratch all those that are softer than it and will be scratched by those that are harder. Only diamond cannot be scratched by any others, so is placed at number 10.

Gemstones that are assigned a mid value (for example, emerald at 7½) do not have a hardness exactly halfway between 7 and 8. They may be scratched by those with a value of 8 (for example, topaz) or more, but scratch gemstones with a value of 7 (for example, quartz) or less.

Mohs’ scale of hardness

Gemstone

1

Talc

2

Gypsum

3

Calcite

4

Fluorite

5

Apatite

6

Feldspar

7

Quartz

8

Topaz

9

Corundum (ruby and sapphire)

10

Diamond

SPECIFIC GRAVITY (SG)

Specific gravity is a value of ‘heft’, how heavy a gemstone feels. It is a ratio, a comparison of the weight of the gemstone with the weight of an equivalent volume of water. The higher the specific gravity, the heavier a gemstone will feel.

REFRACTIVE INDEX (RI)

As light travels from one medium to another it may slow down or speed up, causing the path of the rays of light to alter. As light enters a gemstone it slows down and is refracted (bent). The way that light is reflected at the surface of a gemstone, back towards your eye, or enters the gemstone and is refracted and then is reflected within before coming back out the front of the gemstone towards your eye, will depend on the refractive index of the gemstone and the way in which it is faceted.

Some gemstones, such as diamond, spinel and garnet, are singly refractive:the light ray enters the gemstone and is refracted. Gemstones that have cubic crystals are singly refractive. In doubly refractive gemstones, the light entering the gemstone becomes split into two rays, each refracted (bent) to a different angle. Gemmologists use an instrument called a refractometer to measure the refractive index (RI) of a gemstone, as a means of identification.

BIREFRINGENCE (DR)

Birefringence, also called DR (double refraction), is the difference in the refraction of the rays on entering a doubly refractive gemstone. It is measured using a refractometer and finding the largest and the smallest refractive indices, then working out the difference between the two to give the birefringence. When looking into a gemstone with a high birefringence, bubbles and cracks will appear doubled, as the rays of light have diverged sufficiently to have a noticeable effect.

LUSTRE

Lustre describes the surface appearance of the gemstone. Most gemstones have a glass-like vitreous lustre. Other descriptions include the metallic lustre of hematite, the greasy lustre of turquoise and topaz, and the waxy lustre of amber.

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LIST OF SOURCES

BOOKS

The National Gem Collection by Jeffrey E Post, with photographs by Chip Clark (National Museum of Natural History, Smithsonian Institution in Association with Harry N Abrams, Inc., New York, 1997).

Gemstones (second edition) by Cally Oldershaw, Roger Harding and Christine Woodward (Natural History Museum Publications, London, 2001).

Gemstones (second edition) by Cally Hall (Dorling Kindersley, Eyewitness Handbook, Penguin, London, 2001).

Rocks and Minerals:A Golden Photo Guide from St Martin’s Press by Cally Oldershaw (Elm Grove Books Ltd, New York, 2002).

101 Facts about Planet Earth by Cally Hall and Scarlett O’Hara with additional material by Jen Green (Dorling Kindersley, London, 2003).

Philip’s Guide to Gems by Cally Oldershaw (Philip’s, London, 2003).

Gemstones: Their Sources, Descriptions and Identification (fifth edition) by R Webster with revisions edited by Peter G Read (Butterworth-Heinemann, Stoneham, Massachusetts, 1994).

Jade by Fred Ward (Gem Book Publishers, Malibu, California, 1996).

Rubies and Sapphires by Fred Ward (Gem Book Publishers, Malibu, California, 1995).

Synthetic, Imitation and Treated Gemstones by Michael O’Donoghue (Butterworth-Heinemann, Oxford (1997).

The GIA Diamond Dictionary (third edition), editor in chief Richard E Liddicoat (Gemological Institute of America, Santa Monica, California, 1993).

The Nature of Diamonds by George E Harlow (Cambridge University Press in Association with the American Museum of Natural History, Cambridge, 1998).

Pearls by Fred Ward (Gem Book Publishers, Malibu, California, 1998).

WEBSITES

Smithsonian Institution collection

www.minerals.si.edu/images/gallery/gem.htm

The Gemological Institute of America

www.gia.edu

The Gemmological Association and Gem Testing Laboratory of Great Britain (Gem-A)

www.gagtl.ac.uk

International Colored Gemstone Association

www.gemstone.org

American Gem Society

www.ags.org

American Federation of Mineralogical Societies

www.amfed.org

Mineral Data

www.mindat.org/index-A.html

INDEX

The page numbers in this index relate to the printed version of this book; they do not match the pages of your ebook. You can use your ebook reader’s search tool to find a specific word or passage.

A

Achroite 133

Adularia 74

Alexandrite 54

Almandine 84

Amazonite (microline) 77

Amber 149

Ambroid 151

Amethyst 112

Andradite garnet 86

Andradite (melanite and topazolite) 85

Aquamarine 29

Aventurine quartz 113

Azurite 27

B

Banded agate 36

Beryl 28

Bixbite (red beryl) 34

Black precious opal 105

Bloodstone 52

Blue lace agate 44

Brown quartz 114

Bull’s-eye agate 45

C

Carnelian 51

Cat’s-eye quartz (chatoyant quartz) 115

Chrysoberyl 53

Chrysolite 55

Chrysoprase 49

Cinnamon stone (hessonite) 90

Citrine 118

Colourless orthoclase 74

Colourless sapphire 58

Copal 152

Coral 154

Cordierite 97

Cornelian 45

Corundum 57

Cyclops agate 45

Cymophane 56

D

Demantoid 86

Diamond 66

Dravite 142

Dyed agate 38

E

Emerald 30

F

Feldspar 72

Fire agate 42

Fire opal 106

Fluorite 81

Fortification agate 40

G

Garnet 82

Goshenite 31

Green tourmaline 138

Grossular garnet 88

H

Hawk’s-eye (chatoyant quartz) 116

Heliodor 32

Heliotrope 52

Hematite 96

Hessonite (cinnamon stone) 90

Hope Diamond 11

I

Indicolite (indigolite) 134

Iolite 97

Iris agate 43

Ivory 167

J

Jade 98

Jadeite 99

Jasper 50

Jet 156

L

Labradorite 79

Landscape agate 41

Lapis lazuli 101

Lazulite 102

Logan Sapphire 12

M

Malachite 103

Melanite 85

Microcrystalline quartz (chert and chalcedony) 35

Microline (amazonite) 77

Milky quartz 119

Mocha stone 39

Moonstone 76

Morganite 33

Moss agate 39

N

Nephrite 100

O

Oligoclase (sunstone) 80

Onyx 46

Opal 104

Opalised fossil 107

Orthoclase feldspar 73

P

Padparadscha 60

Paraiba 135

Parti-coloured tourmaline 140

Pearl 158

Peridot 109

Pink sapphire 61

Plagioclase feldspar 78

Plasma 52

Prase 49

Pyrope 92

Q

Quartz 110

R

Rainbow agate 43

Red beryl (bixbite) 34

Rhodochrosite 124

Rhodolite 93

Rhodonite 125

Rock crystal 120

Rose quartz 121

Rosser Reeves Star Ruby 20

Rubellite 137

Ruby 62

Rutilated quartz (sagenite) 122

S

Sagenite (rutilated quartz) 122

Sapphire (blue) 64

Sard 47

Sardonyx 48

Schorl 143

Shell 170

Siberite 136

Spessartine 94

Spinel 126

Stained agate 38

Star of Asia 20

Sunstone (oligoclase) 80

T

Taaffeite (magnesiotaaffeite) 127

Tanzanite 147

Tiger’s-eye (chatoyant quartz) 117

Topaz 128

Topazolite 85

Tourmalinated quartz 123

Tourmaline 130

Tsavorite 91

Turquoise 144

U

Uvarovite 95

W

Watermelon tourmaline 141

White precious opal 108

Y

Yellow orthoclase 75

Yellow sapphire 65

Yellow tourmaline 139

Z

Zircon 145

Zoisite 146

ACKNOWLEDGEMENTS

‘Dedicated to my wonderful daughters, both absolute gems’

Cally Oldershaw is a gemmologist with an international reputation, an examiner for the Gemmological Association of Great Britain and former Curator of Gemstones at the Natural History Museum, London. She has written text books for gemmologists and jewellers worldwide, as well as popular books on topics such as volcanoes, earthquakes, deserts, oceans, mountains, forests, rocks, crystals, minerals, geology and landscapes.

PICTURE CREDITS

GEM HUT (http://www.gemhut.com) page 123; GEOSCIENCE FEATURES PICTURE LIBRARY pages 31, 40, 44, 58, 95, 122, 128, 136; HIRSH pages 60, 61, 62, 65, 70, 86, 90, 130, 135; ICA pages 27, 51, 55, 56, 85, 97, 115, 126, 137, 139, 145, 146; MAGGIE CAMPBELL PEDERSEN pages 149, 151, 154, 156, 158, 160, 162, 167, 169, 170; NATURAL HISTORY MUSEUM pages 23a, 23b, 28, 59, 66, 74, 78, 102, 113, 114, 116, 117, 119, 125, 127, 129, 133, 134, 138, 141, 142, 143, 152; THE SMITHSONIAN INSTITUTION pages 11, 12a, 12b, 20a, 20b, 29, 30, 32, 33, 34, 35, 39, 41, 42, 43, 45, 49, 53, 54a, 54b, 57, 64, 68, 75, 76, 77, 79, 80, 81, 88, 91, 92, 93, 94, 96, 98, 99, 100, 101, 103, 105, 106, 107, 108, 109, 110, 112, 118, 120, 121, 124, 140, 144, 147, 172; V & MUSEUM pages 36, 38, 46, 47, 48, 50, 52, 72, 84, 104.

The Smithsonian would like to thank the following donors: L.T. Chamberlain (page 39);Mrs. W.C. Crane (page 126);A.R. Cutter (page 118);Mr. and Mrs. H. Dibble (page 81);Evyan Perfumes, Inc. (page 29); B.O. Hawk (page 91); Mrs. O. B. James (page 105);Mrs. J. Logan (pages 12a, 64);Mrs. G. M. Morris (page 112);M. M. Post (page 30); R. Reeves II (page 20a);W. A. Roebling (page 107);Helene V. Rubin (page 32);Mr. and Mrs. M. Silverman (page 144);J. Sinkankas (pages 76, 80); M. Stuart (page 124);H. Taylor (page 45);Mr. & Mrs. L. Wilkinson (pages 68, 101);H. Winston, Inc. (page 11).

Edited by Sandra Stafford and Nancy Bailey for Cambridge Publishing Management Limited

Proofread by Jan McCann for Cambridge Publishing Management Limited

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First published in 2006 Great Britain by HarperCollins Publishers Ltd

Text © 2006 Cally Oldershaw

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Source ISBN: 9780007233014
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