Gems and Jewellery

Hematite

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Hematite

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Hematite

Hematite is a compact form of iron oxide. It varies considerably in compactness and form. Its hardest and most compact form is what gets used in jewelery as a gemstone. This is black, and is normally found in massive form as nodules, usually kidney shaped (reniform), sometimes known as kidney ore.
When crushed or powdered it becomes red, and its less compact forms are also red, streak tests are also red.
The compact black forms have specific gravities and hardness at the higher end of the range. The softer forms are used as red pigments, and as jeweler's rouge.

Misnomers

Because of its red streak, it is sometimes known in German as blutstein (bloodstone), but this term is better avoided because of confusion with bloodstone, a variety of chalcedony.

color

Gem quality hematite is black, although some describe it as blue-black.

Sources

One of the main sources is Cleator Moor in Cumbria, England, but it is also found in Elba, the Swiss alps, Germany, Scandinavia, and the USA.
It is carved or polished in Idar Oberstein, but much is now processed in places with lower labour costs.

Imitations

Hematite is sometimes used as beads to imitate black pearls. There are also imitations of haematite, at least one of which produces a red streak.

Hematite in Jewelery

Hematite is often carved as a cameo or sealstone, and is very commonly seen in gent's rings with a crude intaglio carving of a helmeted warrior's head. It is also used as a faceted stone when it resembles black diamond. Because it is opaque, only the top of the stone is faceted, the bottom of the stone is usually left flat.

Garnet

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Garnet

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Introduction

Garnet is a naturally occurring gemstone.Its name comes from Latin granatus meaning seed, because it often resembles small round seeds when found in its matrix rock.Rather than a single gemstone, garnet is a family of related minerals, some of which occur as gemstones.Each has a common crystal structure, and a similar chemical composition.The popular understanding of garnet is as an inexpensive dark red stone. Because it is relatively common and inexpensive, it is often thought of as "only garnet", and as being inferior.This bias extends to other rare and attractive forms of garnet.

Colour

Garnet occurs naturally in a large range of colours including: red, orange, brown, green, yellow, and brown.

Two Families of Garnet

There are two main theoretical groups or "families" of garnet:- pyrope, almandite, spessartite, which are all (metal) aluminium silicates, anduvarovite, grossularite, andradite, which are all calcium (metal) silicates.In practice, there are probably very few garnets with the precise pure chemical composition shown for their type, almost all garnets are of mixed types, where one type is partially replaced by another type.

Trade Terminology

In the trade, gem dealers hardly ever refer to their stock as "pyrope" or "almandite". Instead, they will often refer to "brown" or Indian garnets. As we have stated, very few, if any, pure "types" of garnet occur, most specimens approximate to a particular type.Brown and purpleish "Indian" garnets will usually be towards the pyrope end of the pyrope-almandite axis.Reddish "African" garnets will usually be towards the almandite end of the pyrope-almandite axis.Rhodolite garnets are usually about midway along the pyrope-almandite axis.

Demantoid Garnet

Demantoid garnet is a rare and beautiful bright grass green sub-variety of andradite garnet. It appears to have first been discovered around 1892 in the Bobrovka area of Russia.The Bobrovka is a small tributary of the River Tschussowaja in the Sissersk region on the western side of the Ural Mountains.It was at first thought to be emerald, which is found nearby, and has been erroneously called "Uralian emerald".The name demantoid means diamond-like, because it has a very high adamantine lustre, and a colour dispersion higher than diamond. The only disadvantageous property of demantoid is its low hardness figure at about 6.5 Moh. It is the softest of the garnets, and is more suitable for use in brooches, pendants, or ear-rings, rather than rings, because of this.The brilliant colour of demantoid garnet is due to partial replacement of the silicate by chromic oxide.A diagnostic characteristic of demantoid is the inclusion of radiating fibres of byssolite (asbestos) fibres in a pattern described as a horse-tail. There is no other green stone which shows this feature.In late Victorian times, and early in the twentieth century, demantoid became a very sought after stone. It commanded high prices because it has never been available in large quantity. In recent decades, it has been unobtainable as newly mined stones, and has only been available from antique jewellery.Recently, small finds have again been made in Russia, and a small quantity of fine quality stones have recently come onto the market. Gemstone lovers wishing to acquire a piece of demantoid garnet should take this opportunity to do so. If the current seams of demantoid run out, there may be another century without new stocks of demantoid becoming available.

Tsavolite Garnet

Tsavolite, previously called tsavorite, is a bright green variety of grossular garnet, its colour being induced by the presence of chromium.

Two Families of GarnetThere are two main theoretical groups or "families" of garnet:- pyrope, almandite, spessartite, which are all (metal) aluminium silicates, anduvarovite, grossularite, andradite, which are all calcium (metal) silicates.In practice, there are probably very few garnets with the precise pure chemical composition shown for their type, almost all garnets are of mixed types, where one type is partially replaced by another type.
Trade TerminologyIn the trade, gem dealers hardly ever refer to their stock as "pyrope" or "almandite". Instead, they will often refer to "brown" or Indian garnets. As we have stated, very few, if any, pure "types" of garnet occur, most specimens approximate to a particular type.Brown and purpleish "Indian" garnets will usually be towards the pyrope end of the pyrope-almandite axis.Reddish "African" garnets will usually be towards the almandite end of the pyrope-almandite axis.Rhodolite garnets are usually about midway along the pyrope-almandite axis.
Demantoid GarnetDemantoid garnet is a rare and beautiful bright grass green sub-variety of andradite garnet. It appears to have first been discovered around 1892 in the Bobrovka area of Russia.The Bobrovka is a small tributary of the River Tschussowaja in the Sissersk region on the western side of the Ural Mountains.It was at first thought to be emerald, which is found nearby, and has been erroneously called "Uralian emerald".The name demantoid means diamond-like, because it has a very high adamantine lustre, and a colour dispersion higher than diamond. The only disadvantageous property of demantoid is its low hardness figure at about 6.5 Moh. It is the softest of the garnets, and is more suitable for use in brooches, pendants, or ear-rings, rather than rings, because of this.The brilliant colour of demantoid garnet is due to partial replacement of the silicate by chromic oxide.A diagnostic characteristic of demantoid is the inclusion of radiating fibres of byssolite (asbestos) fibres in a pattern described as a horse-tail. There is no other green stone which shows this feature.In late Victorian times, and early in the twentieth century, demantoid became a very sought after stone. It commanded high prices because it has never been available in large quantity. In recent decades, it has been unobtainable as newly mined stones, and has only been available from antique jewellery.Recently, small finds have again been made in Russia, and a small quantity of fine quality stones have recently come onto the market. Gemstone lovers wishing to acquire a piece of demantoid garnet should take this opportunity to do so. If the current seams of demantoid run out, there may be another century without new stocks of demantoid becoming available.
Tsavolite GarnetTsavolite, previously called tsavorite, is a bright green variety of grossular garnet, its colour being induced by the presence of chromium.

Topazolite

A name used for a variety of garnet with a topaz-yellow or an olive green colour.
MagnetismSome types of garnet, particularly the reddish "African" garnets, which are usually found in close association with diamonds, showing distinct magnetism.
A name used for a variety of garnet with a topaz-yellow or an olive green colour.

Magnetism

Some types of garnet, particularly the reddish "African" garnets, which are usually found in close association with diamonds, showing distinct magnetism.

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Fire Opal

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Fire Opal

A Variety of OpalFire opal is a variety of opal. It is bright orange in colour, and always reminds us of barley sugar sweets. It can vary from completely translucent without any opalescence or iridescence, to semi-translucent with very noticeable flashes of iridescent colour.It is often called Mexican fire opal, because Mexico is one of its prime sources.

Aztec Gold

Fire opal was known to the Aztecs between about 1200 to 1519 AD.

Emerald

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Emerald

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Emerald

Emerald is the grass green variety of the gemstone called beryl. Although all emeralds are beryl, not all beryls are emerald.

Colouration

Pure beryl is colourless, often called white, and although quite rare, tends not to be valuable because it does not have much brilliance. Colours, as in many gemstones, are caused by small amounts of impurity, usually metallic oxides. This is a another case where impurity is desirable.Chromium, in the form of chromic oxide, causes the bright grassy green colouring in beryl, thereby producing emeralds.Vanadium can also affect the exact shade, as may traces of iron.It is also possible to have green beryl which is not emerald, because the colouring agent is not chromium.

Hardness

Emerald, along with other beryls, is quite hard, having a hardness of 71/2 to 8 on Moh's scale, compared with 10 for diamond, 9 for corundum, and 8 for topaz. Hardness is generally a desirable feature is gemstones.

Sources

The earliest known source of emerald was near the Red Sea in Egypt, the so-called Cleopatra's emerald mines. They were probably worked from about 2000 B.C., apparently the location of them was lost in the middle ages, and not rediscovered until 1818. Most emeralds used in ancient jewellery are believed to have come from these mines. They are not worked nowadays because of the low quality of crystals found.Emeralds have been found in Austria since Roman times, in the Legbach ravine at Habachtal near Salzburg. These are no longer commercially mined.Columbia is generally recognised as the source of the world's finest quality emeralds, both in the past and the present. The Columbian Indians were using them before 1537, when Quesada conquered Columbia. Later the Spanish discovered that the emerald mines were at Somondoco, which means "god of the green stones", and which is now known as Chivor. The best coloured Columbian emeralds are said to be those from the Muzo mine, although another mine at Cosquez is also highly rated.Russia has been another important source of emeralds in the past. Most Russian emeralds coming from Sverdlovsk or Ekaterinburg in the Ural Mountains.Emeralds were discovered in Australia in 1890 in New South Wales.Emeralds were discovered between1927 and 1929 at Gravelotte in South Africa, followed by other sources.Another important source of superb quality emeralds, usually only of small size, is Sandawana in Zimbabwe formerly Southern Rhodesia. These were discovered only in 1956.Emeralds were known in India from antiquity, but their source is not certain. The earliest known Indian source was 1929 at Arawalli in Rajahstan, other sources being discovered since. The quality of Indian emeralds is very variable, but most are of lower quality which are often polished as beads.Other sources of emerald include Norway, North Carolina, Connecticut, Maine, New Hampshire, although non of these are very important.

Diamond

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Diamond

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Diamond is Carbon

It may seem surprising that diamond is simply carbon, just like charcoal or graphite. In fact carbon has at least two other rare, and only recently discovered forms, or allotropes, known as fullerenes.
The difference is caused by the different types of bonding between adjacent atoms to form different types of crystalline structure.
In diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral structure, like a pyramid. Each link or bond is the same length, and the tetrahedral formation is therefore completely regular. It is the strength and regularity of this bonding which makes diamond very hard, non-volatile and resistant to chemical attack.
Theoretically a perfect diamond crystal could be composed of one giant molecule of carbon.
Carbon is a non-metallic element with the atomic number of 6, and an atomic Weight of 12. In combination with oxygen and hydrogen it is contained by all living objects. In the form of graphite it appears black or dark gray, opaque, and is very soft, whereas in the form of diamond is it clear, colourless, and extremely hard. In fact diamond is the hardest known naturally occurring substance.
Carbon has a density of about 2.3 and diamond about 3.5.

What Makes Diamond An Ideal Gemstone?

Diamond possesses many qualities which make it an ideal gemstone.
It is extremely hard, and also very tough and hard-wearing, and this also helps it to take a very high polish. Some hard articles are brittle which detracts from their durability. There are some things which are harder than diamond.
In its pure form it is colourless, has a high refractive index, so has a very high lustre.
It possesses high dispersion, meaning that different light wavelengths are diffracted differently, giving a strong scintillating play of prismatic colours.

Diamond Discoveries

Diamonds seem to have been known for about 3,000 years, being mentioned in Exodus chapter 28, however in early times, other hard minerals were often confused with diamond.
It is thought that the earliest diamonds were found in about the 12th century B.C., in India , which remained the most important, if not the sole, source until 1725, when diamonds were discovered in Brazil.
The Indian and Brazilian deposits had been almost exhausted when in 1866, the Eureka diamond was discovered in South Africa, followed by the Star of South Africa in 1869. Shortly afterwards, the great South African diamond rush had started, and South Africa remains one of the world's most important sources of diamonds today.
Diamonds have since been discovered in many other regions of the world, including Russia and Australia.
Until the South Africa finds, diamonds were so rare and valuable, that they were only owned by the very wealthy. They were not available in high street shops!

Why Are Diamonds So Popular?

Through the publicity and promotion given to diamonds largely by the De Beers Company, and through the Diamond Promotion Service, diamonds have become the most desired gemstone.
Thanks to large scale mining, and the development of efficient cutting methods and equipment, diamonds have now become a consumer luxury affordable to the masses.
Mass production jewellery manufacturing techniques have also helped to bring diamond rings and other diamond jewellery into very affordable, even commodity, price ranges.

Man Made

Another fact about diamond which surprises most people, is that more diamond is now manufactured than mined. Synthetically produced diamonds have been made since at least 1954, although the bulk of the synthetic production is used for industrial purposes as diamond grit.
Gem quality synthetic diamonds have also been produced, although it is still more expensive to manufacture them than to mine them.

Colour:

Pure diamond, if such a thing exists, is colourless.
Most diamonds are slightly coloured, even if the colouring is almost imperceptible. The commonest colour is yellow which is caused by tiny amounts of nitrogen being present in the crystal structure, others are gray, light brown or greenish. Diamond can be almost any colour, although strongly coloured attractive specimens are very rare, and as such are not actively promoted by De Beers, probably in case consumers realise that blue, red, green and other colours are attractive, and start buying sapphires, rubies, emeralds and other gemstones instead of diamonds!
As with many gemstones, colours can be artificially produced or modified. Some fancy coloured diamonds are produced by irradiation and subsequent heat treatment. Natural fancy coloured diamonds command very high prices, especially the more more popular colours. Fancy coloured diamonds where the colour has been artificially produced are no less beautiful, but sell for more normal prices.
We occasionally have fancy coloured diamonds available in blue, green, yellow, orange, pink, purple, brown, and even black.

Clarity

It is well known that most diamonds contain slight imperfections or flaws, indeed I firmly believe that there is no such thing as a perfect diamond. The higher the clarity grade of a diamond, the higher its desirability, and therefore its price.

Cut, Proportion, and Shape

Most jewellers will tell you that "cut" is an important factor in the price of a diamond. While this is true, most do not know clearly what they mean by the word "cut". It can have several different meanings.
Firstly, it can describe the shape and facetting pattern of the diamond, as in the modern round brilliant cut, the single or eight cut, pear shape, emerald cut, square, baguette, oval, heart, triangle, princess, marquise or fancy.
Secondly, it can mean the accuracy of the facetting, and the proportions of the stone, and lastly it can apply to the polish or surface finish of the stone.

Demantoid Garnet

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Demantoid Garnet

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Demantoid Garnet

Demantoid garnet is a rare and beautiful bright grass green sub-variety of andradite garnet. It appears to have first been discovered around 1892 in the Bobrovka area of Russia.The Bobrovka is a small tributary of the River Tschussowaja in the Sissersk region on the western side of the Ural Mountains.It was at first thought to be emerald, which is found nearby, and has been erroneously called "Uralian emerald".The name demantoid means diamond-like, because it has a very high adamantine lustre, and a colour dispersion higher than diamond. The only disadvantageous property of demantoid is its low hardness figure at about 6.5 Moh. It is the softest of the garnets, and is more suitable for use in brooches, pendants, or ear-rings, rather than rings, because of this.The brilliant colour of demantoid garnet is due to partial replacement of the silicate by chromic oxide.A diagnostic characteristic of demantoid is the inclusion of radiating fibres of byssolite (asbestos) fibres in a pattern described as a horse-tail. There is no other green stone which shows this feature.

Corundum

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Corundum

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Corundum

Corundum is the mineralogical or gemmological name for aluminium oxide.It is better known for the two closely related varieties of gemstone, sapphire and ruby.
ColoursCorundum can be colourless, red, pink, blue, black, brown, orange, yellow, green, indigo, violet, or mauve. Red corundum and most pink corundum is called ruby, blue corundum is called sapphire, and other colours are also called sapphire, usually with the colour specified as a prefix to the word sapphire, for example, yellow sapphire.

Colouration

Pure corundum is colourless, often called white, and although quite rare, tends not to be valuable because it does not have much brilliance. Colours, as in many gemstones, are caused by small amounts of impurity, usually metallic oxides. This is a case where impurity is desirable.Chromic oxide causes brilliant red colouring in corundum, thereby producing rubies.Ferric oxide causes yellow colouration, titanium oxide produces vivid blue.In fact the colouration of corundum is not quite so simple as this. The titanium and iron are usually present in the form of ilmenite, a mineral which is a titanium iron oxide, TiFeO3. Ilmenite is not isomorphous with aluminium oxide. Isomorphous means being able to replace the host mineral within its crystal structure. Instead ilmenite is present as a microscopic inclusion, in the form of colloidal particles.This colloidal nature may be responsible for other optical effects such as "silk", asterism, and colour banding.

Coral

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Coral

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Organic Gems

Coral is an organic gemstones. Most gemstones are formed from inorganic substances, but a number of gemstones are from organic sources, that is from living things, either plants or animals. Coral is the "skeleton" formed by the individual polyps, plant-like animals, which make up a colony.

Colours

Red and pink are the usual colours for coral, but white and black are also known.

Forms

Coral is usually polished en cabochon or into beads, but is also often carved.

Citrine

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Citrine

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Citrine

Citrine is the clear yellow or golden form of the mineral quartz. As such it is related to amethyst which is the purple form of quartz, and also to rock crystal which is the colourless variety.

Dual Personality

It is possible for some specimens of quartz to be different colours in different areas. Amethyst and citrine are varieties of quart which can both occur in the same stone. As our photograph clearly shows, the difference in colour at the two ends create a striking contrast. Such stones are sometimes called ametrines, but we think they could equally well be called citrysts or citrethysts.

Hardness

The hardness of citrine is 7, and appears on the Moh scale as quartz.

Chrysoprase

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Chrysoprase

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Chrysoprase

Chrysoprase is a green variety of chalcedony which is cryptocrystalline quartz. Its green colour is due to the presence of nickel impurities in the form of oxides or silicates of nickel. It can vary from a greenish yellow to a clear apple green. It is usually cut en cabochon, or into beads, and is also used for intaglios and cameos. Imitations of chrysoprase are made by the staining of agate.

Sources

Chrysoprase was known from ancient Greek and Roman times, although its ancient source is not known. It has been found at Zabkowice in Silesia, the Urals, California, and other parts of the USA.

Chrysoberyl

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Chrysoberyl

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Chrysoberyl

Chrysoberyl is not one of the best known gemstones. Its rarest variety alexandrite, however, is quite well known, although the number of people who have heard of alexandrite is probably 100 times greater than the number who have ever seen one, and 1,000 times greater than the number who have ever owned one.Chrysoberyl is composed of Beryllium Aluminium Oxide, is harder than topaz, and includes a variety known as cat's eye, in addition to alexandrite which we have already mentioned.

Colour

Most chrysoberyl is green or yellow-green, but some is brown. The rare alexandrite shows a colour change from green to red, and cat's eye has a strongly banded appearance which is well described by its name, and is also usually green or yellow-green.

Chalcedony

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Chalcedony

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Chalcedony

Chalcedony is a form of quartz which is cryptocrystalline. Microscopically small crystals of quartz are embedded in opal, which is itself hydrated quartz. The proportion of quartz to opal varies, and this variation is reflected in differing densities, refractive indexes and other properties. The quartz crystals are in a fibrous form, sometimes running approximately parallel to each other, sometimes entwined.Another name for chalcedony is agate, although the term agate is usually used to describe the banded varieties of chalcedony. Many agates are naturally coloured, others are stained for decorative effect. Varieties include chrysoprase, cornelian (carnelian, sard, sardonyx, onyx, plasma, bloodstone, myrickite. There are many differently named varieties of agate depending on their appearance such as moss agate, fossilised wood. and other forms of fossil. Jasper also belongs to this group, and contains impurities which cause heavy pigmentation.

Cat's Eye

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Cat's Eye

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Cat's Eye

True cat's eye is a variety of chrysoberyl, sometimes called cymophane, and as such is related to alexandrite.It is a rare and valuable gemstone, which is often underrated as being a "semi-precious" stone.

Chatoyancy

Chatoyancy or chatoyance, literally from French means cat's eye. It is the effect seen best in this variety of chrysoberyl, but also found in a few other gemstones. The effect is a strongly banded one caused by tube-like or needle-like crystals running along the length of the stone.Other stones which show chatoyancy include sapphire and tourmaline.Chatoyancy is related to asterism.

Cabochons

Cat's eye chrysoberyls are always cut as cabochons to show off their spectacular effect to it best.

Colour

Cat's eye chrysoberyl is green or yellow-green, yellow, or brown to yellow-brown

Cornelian

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Cornelian

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Cornelian

Cornelian is a red variety of chalcedony which is cryptocrystalline quartz. Its red colour is due to the presence of iron impurities in the form of iron oxide or hematite. It can vary from a flesh red to a clear red. It is usually cut en cabochon, or into beads, and is also used for intaglios and cameos. Imitations of cornelian are made by the staining of agate.

Sources

Originally found in the deserts of Arabia and Egypt, it has also been found in the Rio Grande area, India, China, Colombia, Saxony, Scotland, West Germany and USA.

Bloodstone

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Bloodstone

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Bloodstone is a variety of chalcedony which is cryptocrystalline quartz. It is green plasma containing red spots of jasper, which look like spots of blood giving the stone its descriptive name. The green colour is due to the presence of masses of chlorite, and the red spots are inclusions of red coloured jasper. It is usually cut en cabochon, or into beads, but most often used as a sealstone, and is popular in gents' signet rings. It is often quite coarse and therefore is closely related to jasper, another group of quartz.
It is also called heliotrope although this name is hardly ever used nowadays.
The name bloodstone is sometimes misleadingly used for haematite.

Sources
The best bloodstone is obtained from India, other sources include USA, Brazil, and Australia.

Beryl

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Beryl

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Varieties

Beryl exists in a number of different varieties, some being better known by their own name, for example, emerald is the grass green variety and aquamarine is the sky blue variety.

Colouration

Pure beryl is colourless, often called white, and although quite rare, tends not to be valuable because it does not have much brilliance. Colours, as in many gemstones, are caused by small amounts of impurity, usually metallic oxides. This is another case where impurity is desirable.Chromium, in the form of chromic oxide, causes the bright grassy green colouring in beryl, thereby producing beryls.Vanadium can also affect the exact shade, as may traces of iron.It is also possible to have green beryl which is not emerald, because the colouring agent is not chromium.

Hardness

Beryl is quite hard, having a hardness of 71/2 to 8 on Moh's scale, compared with 10 for diamond, 9 for corundum, and 8 for topaz. Hardness is generally a desirable feature is gemstones.

Cleaning

Beryl jewellery can be carefully cleaned using warm soapy water, or detergent, rinse thoroughly afterwards as detergents can cause dermatitis and allergic reactions. Enzyme cleaners should be avoided for the same reasons. Brushing with an old tooth brush to remove dirt and grease will also help. Cleaning agents containing chlorine may have a detrimental effect on low carat gold alloys, so are best avoided.We stress that reasonable care should be taken when cleaning emeralds, as washing with strong detergents could cause any oil to be diluted or removed, requiring the stone to be re-oiled.Beryls do not like excessive heat, and although they can tolerate temperatures above 100c (the boiling point of water), it is advisable to use warm water rather than hot water, to reduce the dangers of thermal shock.It is not advisable to clean beryl in an ultrasonic tank. We sometimes risk it with our own stock, but we would never clean a large or valuable beryl which did not belong to us, in an ultrasonic machine.

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Aquamarine

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Varieties

Aquamarine is the sky blue or sea blue variety of beryl, sometimes it is sea green, and less desirable.The word aquamarine literally means seawater, and is very frequently shortened to aqua.

Colouration

The colour of aquamarine is due to the presence of traces of iron present as an impurity in the crystal structure of beryl.

Heat Treatment

As with many gemstones, the colour of aquamarine has almost always been improved by treatment of some kind. Heat treatment is used for aquamarines, to turn greenish, yellow or brown stones into a beautiful blue. The stones are heated to about 400 to 450 degrees Celsius, and the colour change is permanent.

Colour Saturation & Size

Even the best aquamarines are fairly pale compared with other gemstones such as sapphire. Large stones benefit from the effects of colour saturation, and as aquamarine, unlike emerald, tends to form quite large clear crystals, this means that large aquamarines are relatively easy to find, and the price does not rise so steeply with size as it does with many other stones.It also means that small stones often lack colour intensity and are therefore not as attractive. Small aquamarines with good colour are therefore harder to obtain, and relatively expensive for their appearance. For small stones it may be preferable to use Ceylon sapphire instead.

Hardness

Aquamarine is quite hard, having a hardness of 71/2 to 8 on Moh's scale, compared with 10 for diamond, 9 for corundum, and 8 for topaz. Hardness is generally a desirable feature is gemstones.

Prices

The price range of aquamarine is very large, ranging from a few pounds per carat.

Cleaning

Aquamarine jewellery can be carefully cleaned using warm soapy water, or detergent, rinse thoroughly afterwards as detergents can cause dermatitis and allergic reactions. Enzyme cleaners should be avoided for the same reasons. Brushing with an old tooth brush to remove dirt and grease will also help. Cleaning agents containing chlorine may have a detrimental effect on low carat gold alloys, so are best avoided.We stress that reasonable care should be taken when cleaning emeralds, as washing with strong detergents could cause any oil to be diluted or removed, requiring the stone to be re-oiled.Aquamarines do not like excessive heat, and although they can tolerate temperatures above 100c (the boiling point of water), it is advisable to use warm water rather than hot water, to reduce the dangers of thermal shock.It is not advisable to clean aquamarine in an ultrasonic tank. We sometimes risk it with our own stock, but we would never clean a large or valuable aquamarine which did not belong to us, in an ultrasonic machine.

Apatite

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Apatite

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Apatite

Apatite is a common mineral with a wide and attractive range of colours. In non-gem quality, very large crystals occur weighing up to several hundredweight. Clear gem quality crystals, though, are quite scarce and always small. It is too soft to be commonly used in jewellery, particularly in rings. It sometimes occurs with chatoyancy (cat's eye effect).

Colour

Colourless (white), pink, yellow, green, blue, and violet.

Andalusite

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Andalusite

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General

Andalusite is an attractive and unusual gemstone, first discovered in Andalucia, Southern Spain, after which it is named. It has some similarities with the very rare and valuable alexandrite, as it is strongly pleochroic, about which more later. It is suitable for use in jewellery as it is quite hard. The fact that it is seldom seen in jewellery is probably because it is quite rare, and most people, even in the jewellery industry, have never heard of it, let alone seen it. Strangely enough, some years ago we had just finished making a ring set with a central andalusite, when another local jeweller visited us. I am sure he will not mind me identifying him as Russell Fielding. I showed him the ring, and fully expected him not to know what the stone was, when he floored and impressed me by saying without any hesitation that it looked like andalusite.

Colour

Many andalusites display different colours within the same stone. This is due to its pleochroism, which we will now explain by quoting from Robert Webster's "Gemmologists' Compendium":-
PleochroismThe differential selective absorption of the ordinary ray and the extraordinary ray in uniaxial stones (dichroism), or of the three rays corresponding to the three principal vibration directions in biaxial stones (trichroism). Of course, to the non-gemmologist, this explanation probably creates more confusion than clarification. It relates to the way light is refracted when passing through a stone.Interestingly, "An Illustrated Dictionary of Jewellery" by Harold Newman describes andalusite as having strong dichroism, which is clearly incorrect as andalusite is biaxial not uniaxial, and therefore must be trichroic not dichroic. Although we find Newman's book useful, it contains numerous errors and omissions.Typical colours for andalusite are green, brown, red, greenish-brown, brownish-green. Its pleochroic colours are red, green and yellow.Because of the pleochroism, the colour of an andalusite can be affected considerably by the direction in which it is cut.Our photograph is disappointing and deceptive. The actual stone is a pleasant greenish brown to red. We used flash lighting with a digital camera, followed by software adjustment of the lighting levels, and the effect was to make the stone appear quite a dull brownish colour. Who said the camera never lies?

Star Andalusite or Chiastolite

An impure variety of andalusite known as chiastolite contains carbonaceous inclusions in a cruciform arrangement. These are cut and polished for use as amulets in many countries, largely because of the symbolism of the cross.

Sources

Although as we have already noted, andalusite was originally discovered in Andalucia, it is also found in Brazil, Sri Lanka (Ceylon), Siberia, Brittany, Australia and the USA. Small non-gem crystals are also found in Cumbria, UK.

Amethyst

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Amethyst

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Amethyst

Amethyst is the clear purple, mauve or violet form of the mineral quartz. As such it is related to citrine which is the yellow form of quartz, and also to rock crystal which is the colourless variety.

What's in a Name?
Amethyst gets its name from a Greek word amethustos meaning "not drunken", as it was believed to protect against intoxication by alcohol.It would be interesting to test this ancient theory whilst being breath-tested, but don't cite us in your defence.

Too Cheap?

One thing about amethyst that we find very strange is that some people complain about its low price. Compared with diamond, ruby, emerald and sapphire, it is true that amethyst is inexpensive, particularly in lower qualities. Even in very high qualities, amethyst is still not expensive, which makes it a veritable bargain among gemstones. We cannot understand why it is necessary for a gemstone to be rare and valuable before people can appreciate its beauty, even though we list rarity and value among the attributes of gemstones on our Gemstone Characteristics page. In fact, high quality amethysts still add up to a lot of pounds. This also seems to surprise some folk. Just because some amethysts are cheap, they assume this must be the case for all amethysts. Also because some amethysts are cheap, other people don't want to own even a high quality attractive amethyst, possibly because their friends may regard amethysts as not valuable. It's a bit like refusing to accept a Picasso because the artist is offering to give it to you for nothing, instead of asking a couple of million pounds for it.In our experience there are, sadly, many people who can only judge quality by its price tag. Often these same people spend half their life searching around for the best deal, but fail to see it when they fall over it.

Amber

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Amber

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Amber
Amber is one of the organic gemstones, being the time-hardened fossilized resin of pine trees, the now extinct pinus succinifera, and others. As such it varies from about 20 to 60 million years old, according to different sources. It appears surprisingly light and warm to the touch, and readily produces static electricity when rubbed. Indeed it was known to the ancient Greeks as elektron, and it is from this that we have obtained the word electron for the negatively charged particle, and also the word electricity. The metal electrum was so called because of its similarity in colour to amber. Amber is known in German as bernstein because in the middle ages, powdered amber was burnt as an aromatic incense.
Colour
Amber is most usually similar colours to honey, varying from golden yellow, through rich orange and red to brown, but some can be white, dark brown almost to black, blue or green.

Amazonite or Amazonstone

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Amazonite or Amazonstone

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Amazonite or Amazonstone
Amazonite is a gem variety of microcline feldspar, being potassium aluminium silicate. It is usually polished as a cabochon.In common with other feldspar gems, it displays a schiller of coloured light, caused by inclusions or its crystal structure creating interference effects of light.It is sometimes called amazonstone or amazon stone, possibly because one of its sources is Brazil, although not from the Amazon regions.
Colour:Amazonite varies from bright verdigris green to a bluish green.

Alexandrite

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Alexandrite

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Alexandrite
Alexandrite is a Rare Variety of ChrysoberylAlexandrite was discovered near Ekaterinburg in the Ural Mountains in Russia in 1830, and was named after Alexander II. Other sources now include Sri Lanka, Burma, Brazil, Zimbabwe, Madagascar and North America.The important feature of Alexandrite which makes it highly unusual and collectable amongst gemstones is its strong colour change when viewed in different lights. Many other stones show a similar property, but nowhere as strongly, and not with such highly contrasting colours.It is hardly ever seen in the U.K. because of its rarity and high price.
Colour:Chrysoberyl is mainly green, yellow or brown. High quality alexandrite varies from grass green to raspberry red, although some stones will tend towards olive green or brown, and others to yellow. The red and green colouration is caused by the partial replacement of aluminium by chromium.In daylight, stones appear green, whilst in tungsten lighting they will change colour to red. This effect is caused by a combination of factors. Alexandrite is bi-refringent (doubly refractive), and bi-axial, so that it possesses three different refractive indexes in its three different optical directions. Each of these three directions has a strongly different absorption spectrum, causing different colours to be seen when viewed from different directions in relation to the crystal structure, an effect known as pleochroism. Daylight contains high proportions of blue light, tungsten lighting contains a higher balance of red light. The two main optical directions of alexandrite absorb light of different wavelengths in considerably different ways. If this sounds technical and complicated, it is because it is technical and complicated. I will try to return to this paragraph later when I have worked out a simpler sounding way to explain the phenomenon. Any suggestions welcome.

Agate

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Agate

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Agate

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Agate is the name given to a wide selection of varieties of chalcedony, a form of quartz which is cryptocrystalline. Microscopically small crystals of quartz are embedded in opal, which is itself hydrated quartz. The proportion of quartz to opal varies, and this variation is reflected in differing densities, refractive indexes and other properties. The quartz crystals are in a fibrous form, sometimes running approximately parallel to each other, sometimes entwined.The names for chalcedony and agate are somewhat interchangeable, although the term agate is usually used to describe the banded varieties of chalcedony. Many agates are naturally coloured, others are stained for decorative effect.
Varieties and ColoursAgate can be many different colours, and because its banding is so variable, different types of it have been given many different descriptive names. It is often used to make quite large decorative items. Some names include moss agate and picture agate. Many types of organic material have been fossilised by agate, where the organic material has been replaced slowly over a long period of time, so that the original structure of the original item is retained. Fossilised or petrified wood is an attractive form of agate.
Geodes and Thunder EggsAgate is frequently found in the form of rounded nodules or geodes. When split or sliced, these show their banding to good, sometimes startling effect. In some geodes there is a central cavity, in other the centre is hollow. This provides an important clue to the formation of such geodes.The Indians (sorry, Native Americans) of the western American states called agate nodules "thunder eggs", a wonderfully romantic and descriptive name.

Choosing a Gem

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A gemstone is the naturally occurring crystalline form of a mineral, which is desirable for its beauty, valuable in its rarity and durable enough to be enjoyed for generations. There are more than 40 popular gem varieties and many more rare collector gemstones. Although some gemstone varieties have been treasured since before history began and others were only discovered recently, they are all nature's gifts to us.Please enjoy surfing through our Gem by Gem list of the worlds most fascinating gemstone varieties.