Alexandrite
This rare gemstone was named after the Russian tsar Alexander II when it was first discovered in the emerald mines near the Tokovaya River in 1834.
The stone’s most striking feature is its ability to change colour from green or bluish-green in daylight to a soft shade of red, purplish-red or raspberry red in incandescent light.
The best alexandrites should show a vivid bluish-green in daylight and a purplish-red in artificial light without any trace of undesirable brown or grey – the more distinct the change of colour, the more valuable the stone.
Today the Russian supply of alexandrites is believed to be exhausted but the stone is still sourced from Brazil, Sri Lanka, India, Burma, Madagascar and Zimbabwe.
All alexandrite is rare and valuable but alexandrite from Russia is still the most desired of all – and finely faceted alexandrites above one carat are among the most expensive gemstones in the world.
 
Amethyst
 
The amethyst is extravagance in violet. For many thousands of years, the most striking representative of the quartz family has been a jewel coveted by many – in fact the Russian Empress Catherine the Great sent thousands of miners into the Urals to look for it.
The amethyst has the same hardness, refraction and weight as other quartzes but its crystal structure is stratified so areas and lamellae of varying colour intensity are often formed in the stone. This is the reason why there are relatively few large cut amethysts with an evenly distributed dark colour despite the fact that the stone is abundantly in all parts of the world
The Amethyst deposits with the greatest economic significance are sourced from southern Brazil, Uruguay and Madagascar  –most beautiful amethyst with the deepest colour comes from Uruguay but it is mostly blemished.
 
 Aquamarine 
 
From the light blue of the sky to the deep blue of the sea, aquamarines shine over an extraordinarily beautiful range of mainly light blue colours.
Not surprisingly the stone’s name is derived from the Latin ‘aqua’ (water) and ‘mare’ (sea).
Aquamarine, which is one of the world’s most popular and best-known gemstones, belongs to the beryl family and is thus closely related to the emerald
The stone has good hardness (7.5 to 8 on the Mohs scale), is almost entirely free of inclusions and has a wonderful shine.
Iron is the substance which gives aquamarine its blue colour – the more intense the colour, the more valuable the stone is.
Many colour nuances of aquamarine have melodious names: the rare, intense blue aquamarines from the Santa Maria de Itabira mine in Brazil are called ‘Santa Maria’, the aquamarines from Africa are referred to as ‘Santa Maria Africana’ and Brazil’s less intense blue stones are called ‘Espirito Santo’
Aquamarines are also found in other countries including Nigeria, Zambia, Madagascar, Mozambique, Afghanistan and Pakistan.
 
Citrine
Many people have come to know and love this stone under the name of gold topaz, Madeira topaz or Spanish topaz, but citrine has little in common with topaz except for a few nuances of colour.
The citrine is a member of the large quartz family. Its name refers to the yellow colour of the lemon although the most sought-after stones have a clear, radiant yellowish to brownish red.
Like all crystal quartzes, the citrine has a hardness of 7 on the Mohs scale and is thus, to a large extent, insensitive to scratches.
The yellow coloured stones do occur naturally where there are traces of iron in the stone’s silicon dioxide but this is a very rare occurrence  and most citrines on the market today are in fact heat-treated or ‘burnt’ amethysts or smoky quartzes – only a trained specialist can recognize the “subtle stripes” of colour associated with the heat treated stones.
 
Emerald
Emeralds are the greenest of all gemstones and therefore is apt that its name comes from the Greek ‘smaragdos’ via the Old French ‘esmeralde’ which really just means ‘green gemstone’.
From a chemical-mineralogical point of view, emeralds are beryllium-aluminium-silicates with a hardness of 7.5 to 8 on the Mohs scale.
Good quality emerald is fairly rare as inclusions often mar the evenness of the stone’s colour.
However, fine inclusions do not diminish the value of a good coloured emerald. For example even with inclusions, an emerald in a deep, lively green still has a much higher value than an almost flawless emerald whose colour is paler.
Colombia continues to be the main supplier of the world’s best emeralds (fine shining emerald green unimpaired by any kind of bluish tint) but fine emeralds are also found in other countries including Zambia, Brazil, Zimbabwe, Madagascar, Pakistan, India, Afghanistan and Russia.
 
Garnet 
 
 
Most people think a garnet is a deep red gemstone but the term ‘garnet’ actually refers to a group of more than ten different of gemstones (including almandine, andradite, demantoid, grossularite, pyrope, rhodolite and tsavorite), which are also available in green, yellow, orange and brown hues.
Furthermore, the world of the garnet is also rich in stones whose colours change depending on whether they are seen in daylight or artificial light.
Nonetheless despite such big differences in appearances, all garnets have a similar chemical composition which includes a hardness of 7-7.5 and a high refractive index.
The most popular red coloured garnets include fiery red pyropes, dark red almandines, velvety red rhodolitse with a fine violet or raspberry-red undertone, and the radiant orange to red spessartites (mandarine garnet).
The rarer green varieties of garnet include grossularite in many fine tones of yellow, green and brown, tsavorite  with its vivid and light to deep and velvety green, and the demantoid (with a brilliance even greater than that of the diamond).
Most garnets today come from African countries but they are also found in India, Russia and Central and South America.
 
Kunzite
The appeal of this young gem, which wasn’t discovered until 1902, lies in its clarity and its fine delicate pink nuances which often display a hint of violet
In order to make sure that the fine colour is shown to its full advantage, the cutter must align the raw crystal very precisely as a kunzite can appear violet, pink or even colourless depending on the angle from which it is viewed.
In a well cut stone, the most beautiful colour nuance will always be visible from above.
In the trade kunzite is one of the few gems which are available in relatively large sizes at affordable prices. However it should always be remembered that it is first the colour and then the clarity which determines the stone’s value. The more intense the colour, the more valuable the kunzite.
The question of whether the colour should tend more or less strongly towards violet depends on personal preference.
Today, kunzite is mainly found in Afghanistan, Madagascar, Brazil and the US. The crystals, or fragments of crystals, can attain sizes of up to several kilograms.
 
Lapis lazuli
Lapis lazuli was one of the first gemstones to be worn as jewellery. At excavations in the ancient centres of culture around the Mediterranean, archaeologists have again and again found grave furnishings, decorative chains and figures made of lapis lazuli – clear indications that the deep blue stone was already popular thousands of years ago among the people of Mesopotamia, Egypt, Persia, Greece and Rome. 
Mainly consisting of diopside and lazurite, uncut lapis lazuli is usually a matt deep dark blue colour, often with golden inclusions (pyrites) and whitish marble veins. The blue colour comes from the sulphur content of the lazurite and may range from pure ultramarine to a lighter blue.
The price of lapis lazuli varies greatly depending on the beauty and intensity of its colour. The most desirable colour is an intense, deep blue. Finely distributed pyrite crystals that shimmer like gold sequins increase the value of the gemstone, while a restless, rough or blotchy grain reduces it.
The best lapus lazuli comes from the north-east of Afghanistan although it is also found in Russia, Chile, Italy, Mongolia, the USA, Canada, Burma (Myanmar) and Pakistan.
 
Moonstone
The moonstone is characterised by an enchanting play of light. Indeed it owes its name to that mysterious shimmer which changes constantly when the stone is moved.
Moonstones from Sri Lanka shimmer in pale blue on an almost transparent background while specimens from India feature a nebulous interplay of light and shadow on a background of beige-brown, green, orange or brown.
Moonstone belongs to the large mineral group of the feldspars and is also sometimes known as ‘adularia’ or ‘selenite’.
The shimmer of light, or ‘adularisation’, on the moonstone is caused by the lamellar inner construction of the gemstone which scatters and refracts incident light rays.
However, perhaps surprisingly, that defining shimmer of light is rarely visible in the uncut stone.
Therefore, classical moonstones are always cut as cabochons with the axes of the crystal precisely aligned into the zenith of the stone to maximize this desired light effect.
The most highly valued moonstones are those which are larger, more transparent and more intense in colour.
Really fine blue specimens display an incredible ‘three-dimensional’ depth of colour which the observer cannot really see unless the stone is moved about in a playful way.
 
Opal 
 
 Although there are many varieties of fine opals all but one display the ‘opalising’ effect and shine and sparkle in a continually changing play of colours.
Opals are simply a combination of silica and water, or to be more precise, opals are a gel from silica mixed with varying percentages of water
The famous ‘opalising’ effect is caused by small silica gel spheres which dissect light on its passage through the gemstone and turn it into all the colours of the rainbow.
In order to best bring out the play of colour in a fine opal, the stones are cut and polished to round or oval cabochons, or other softly domed shapes.
Some of the most popular opal types are dark or black opal, white or light opal, milk or crystal opal, boulder opal, opal matrix, Yowah Nuts, Mexican opal and fire opal.
The latter is the only opal which does not show the ‘opalising effect’ but is nonetheless still considered a fine opal – other opals which lack the typical play of colours are simply called ‘common opals’.
Australia is the world’s most important supplier of fine opals – almost 95 percent of the world’s supply comes from local mines. The remaining five per cent are mined in Mexico, in Brazil’s north and in the US states of Idaho and Nevada.
 
Peridot
This gemstone has three names ‘peridot’, ‘chrysolite’ and ‘olivine’ but it is one of the few gemstones which come in one colour only – a rich green with a slight tinge of gold
From a chemical point of view, peridot is an iron magnesium silicate. The intensity of the colour depends on the amount of iron actually present and the colour itself can vary over all shades of yellowish green and olive through to brownish green.
Peridot is not particularly hard (only 6.5 to 7 on the Mohs scale) but it is nonetheless fairly robust.
The most beautiful stones come from the border area between Pakistan and Afghanistan. However, the peridot is also found in Myanmar, China, the US, Africa and Australia. Stones from East Burma (Myanmar) have a vivid light green colour and fine inclusions with a silky shine to them while peridot from Arizona often has somewhat yellowish or gold-brown nuances.
The peridot is mostly faceted but cabochons are made if the material contains more inclusions as the domed cut brings out the best of the fine silky shine of the inclusions.
 
Quartz
Quartz is one of the most popular and most affordable gemstones on earth.
Indeed throughout history, quartz has been the common chameleon of gemstones, often standing in for more expensive gemstones in jewellery pieces.
Fortunately though the incredible variety of quartz (which includes amethyst, citrine, ametrine, onyx, agates and jasper) is now beginning to be appreciated in its own right.
The transparent, colourless variety of quartz is known as ‘rock crystal’ while coloured transparent varieties include rose quartz (pink), smoky quartz (brown), amethyst (purple to violet), citrine (yellow to orange) and ametrine (purple and yellow).
While most varieties of transparent quartz are valued most when they show no inclusions, some are valued chiefly because of them. For example rutilated quartz is transparent rock crystal with golden needles of rutile arrayed in patterns inside it and tourmalinated quartz features black or dark green tourmaline crystals.
Quartz that is formed not of one single crystal but a number of finely grained microcrystals is known as chalcedony.
The variety of chalcedonies is even greater than that of transparent quartz and includes cryptocrystalline quartz, agates, bloodstone, jasper and black onyx.
 
Ruby
 
In the fascinating world of gemstones, the ruby is the undisputed ruler.
For thousands of years, the red stone has been considered one of the most valuable gemstones on earth. It has everything a precious stone should have – magnificent colour, excellent hardness and outstanding brilliance.
Ruby is the red variety of the mineral corundum, one of the hardest minerals on earth.
The colour of ruby is the most important factor is determining its value. Its transparency is only of secondary importance so inclusions do not impair the quality of a ruby unless they decrease the transparency of the stone or are located right in the centre of its table.
The most desired of all colours is the ‘Burmese ruby’. The term does not mean that a ruby originated in Burma but that its colour is that of stones typically found in the famous deposits of Burma (Myanmar) – a rich, full red with a slightly bluish hue.
Finally as fine rubies are extremely rare particularly in sizes larger than 3 carats, good coloured rubies in large sizes with hardly any inclusions are considered more valuable than similarly-sized diamonds.
 
Sapphire
 
Blue sapphires are the world’s best known sapphires but they are not the only sapphires –yellow, pink, orange, green and purple sapphires also exist.
The sapphire belongs to the corundum group of gemstones. All the stones in this group are made from pure aluminium oxide combined with a small amount of other elements, especially iron and chrome, which are responsible for turning crystals that were basically white into blue, red, yellow, pink or greenish sapphires.
However, this does not mean that every corundum is also a sapphire. Years ago gem specialists agreed that ruby-red sapphires, which are coloured by chrome, should be called ‘rubies’ and all those which were not ruby-red should be called ‘sapphires’.
Specialists and connoisseurs regard the Kashmir colour (an intense blue with a very subtle violet undertone intensified by a fine, silky shine) as the most beautiful and most valuable blue.
Sapphires are found in India, Burma, Ceylon, Thailand, Vietnam, Australia, Brazil and Africa.
 
Spinel
 
Spinel is the great impostor of gemstone history – many famous rubies in crown jewels around the world are actually spinels. The most famous is the Black Prince’s ruby, a magnificent 170-carat red spinel that now adorns the Imperial State Crown of England in the British Crown Jewels.
In Burma (Myanmar), where some of the most beautiful colours are mined, spinel was recognised as a separate gem species as early as 1587 but in other countries the masquerade went on for hundreds of years.
Now treasured for its own sake, spinel is valued for its brilliance, hardness and wide range of spectacular colours. In addition to beautiful rich reds, spinel can be found in pastel shades of pink and purple as well as a hot pink with a tinge of orange.
Spinel also comes in beautiful blue tones called cobalt spinel, but these are very, very rare.
In fact, the main factor preventing the spinel from achieving greater recognition is its rarity. Fine spinels are now rarer than the rubies they used to imitate.
In addition to Burma, spinel is mined in Sri Lanka, Tanzania and Tadzhikistan.

Tanzanite
 
Thanks to its extraordinary blue colour, limited supply and a little help from Tiffanys, tanzanite is one of the most coveted gemstones in the world.
Discovered in 1967 in the east Africa’s Tanzania, tanzanite is a blue zoisite which consists of calcium aluminium silicate.
The stone’s blue colour varies from ultramarine blue to light violet-blue but its most desired colour is a blue surrounded by a delicate hint of purple.
Tanzanite also has well developed polychromaticity so that depending on the angle from which you look at it, the stone may appear blue, purple or brownish-yellow.
When first discovered the stone was simply called ‘blue zoisite’ but Tiffany’s proposed the name ‘tanzanite’ as it felt ‘blue zoisite’ was too similar to suicide and then began publicizing the new gem with a broad-based advertising campaign.
Today the gemstone, which is still only found in the one mine in Tanzania, is cut in every imaginable shape from the classical round shape to a number of imaginative designer cuts.

Tourmaline
 
Tourmalines out performs all other precious stones with its broad spectrum of colours. There are tourmalines in almost every hue from red to green and from blue to yellow. There are tourmalines that display two or more colours and there are tourmalines which change their colour when the light changes from daylight to artificial light.
Yet there are no two tourmalines that are exactly alike.
In essence tourmalines are mixed crystals of aluminium boron silicate with a complex and changing composition – so much so that even slight changes in the composition create completely different colours in the stone.
In addition the gemstone not only boasts a rainbow of colour possibilities but also marked dichroism – the colour looks different or more or less intense depending on the angle from which it is viewed.
Tourmalines are found almost all over the world including Brazil, Sri Lanka, south and south-west Africa, Nigeria, Zimbabwe, Kenya, Tanzania, Mozambique, Madagascar, Pakistan, Afghanistan and the US.
Although there are plenty of gemstone deposits which contain tourmalines, good qualities and fine colours are not often discovered among them. For this reason, the price spectrum of the tourmaline is almost as broad as that of its colour.
 
Topaz
This gemstone comes in yellow, yellow-brown, honey-yellow, flax, brown, green, blue, light blue, red and pink – or no colour at all.
Yellow topaz is often confused with the more affordable citrine which is often incorrectly called gold topaz.
However there are major differences between topaz and the cheaper yellow stone.
Topaz is a fluorine aluminium silicate in chemical terms and thus considerably harder heavier and more refractive than quartz.
In addition, unlike citrine which is available only in yellow and reddish-brown hues, topaz can be found in all the colours of the rainbow. 
Today topaz is often given the additional predicate ‘pure’ in the jewellery industry to make it clear that the stone being referred to is topaz rather than yellow quartz (otherwise known as gold topaz or citrine).
Topaz can be found in Russia, Afghanistan, Sri Lanka, Czech Republic, Germany, Norway, Pakistan, Italy, Sweden, Japan, Brazil, Mexico, Flinders Island and the US.
 
Turquoise
 
Turquoise has been esteemed for thousands of years as a holy stone, a bringer of good fortune or a talisman but the precious gemstone is not always turquoise in colour – it ranges sky blue to grey-green hues.
Turquoise is a copper aluminium phosphate with a hardness of just 6 on the Moh’s scale. The blue colour is created by copper, the green by bivalent iron and chrome.
Often, turquoise has veins or blotches running through it, which are brown, light grey or black. These lively, more or less regular patterns, are known as ‘turquoise matrix’ but the crystals are microscopically small and can hardly ever be seen with the naked eye.
The best quality turquoises are of a pure, radiant sky blue, a colour which is highly esteemed with or without its fine regular matrix.
The more strongly a stone’s colour tends toward green and the blotchier and more irregular its matrix, the less the stone is likely to be worth.
The most well known turquoise deposits are found in the US, Mexico, Israel, Iran, Afghanistan and China. The most beautiful turquoises, in a splendid light blue, come from deposits in the north of Iran.
 
 
Zircon
 
  
Zircon occurs in a wide range of colours, but for many years the most popular was the colourless variety, which looks more like diamond than any other natural stone because of its brilliance and dispersion.
Today the most popular colour is blue. Most blue zircon is a pastel blue, but some exceptional gems have a bright blue colour. Zircon is also available in green, dark red, yellow, brown and orange.
Natural zircon today suffers on account of the similarity of its name to cubic zirconia, the laboratory-grown diamond imitation. In fact many people are unaware that there is a natural gemstone called zircon.
Zircon is mined in Cambodia, Sri Lanka, Thailand, Myanmar, Australia and other countries.
The wide variety of colours of zircon, its rarity, and its relatively low cost make it a popular collector’s stone.
 

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