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Faking the Grail

Identifying Gems

Some of the most valuable diamonds in the world


These are some of the most valuable diamonds in the world. They all have names and pedigrees, some of them stretching back centuries.

A few, which came from India originally, have always been owned by kings and emperors and have been used as tribute and as collateral, seized by conquest, hidden during revolutions, lost, stolen and rediscovered over the years and now reside in national museums and collections of Royal regalia, past and present, from Moscow to London.

Most of the precious stones come in a variety of colours. Identifying them by colour alone is extremely difficult. The colour of any stone depends on the minerals present within it. Glass, which depends on metallic oxides for its colour, has been used since time immemorial to make paste jewels, which can easily be mistaken for the real thing, even by an educated eye.

Topaz, sapphire, zircon, emerald, citrine and diamond

"Topaz"

Historically there was a tendency to call all yellow gemstones topaz, whether they were:

"Rubies"

Rubies, garnets, spinel, zircon, tourmaline and diamond

Similarly, all the red gemstones were referred to as rubies, whether they were:

The Black Prince's Ruby in the British Crown Jewels is actualy a red spinel that was first recorded when it belonged to a Moorish Prince of Granada, in the middle of the fourteenth century. Originally intended to be worn as a pendant in the Oriental style, it has been pierced for that purpose. A small ruby has been set on top to hide the hole.

Another famous spinel, the Timur Ruby, which is also in the British Crown Jewels, is engraved with Persian inscriptions in Arabic script recording the names of five previous owners including Jehangir Shah and Shah Jehan.

"Emeralds"

Emeralds, aquamarine, peridot, tourmaline, demantoid garnet and diamond

Green gemstones historically referred to as emeralds include:

Rumour has it that the Roman Emperor Nero had a pair of emerald sun glasses, which is highly unlikely, because the size and quality of the emeralds available probably weren't particularly suitable for lenses of any kind. All emeralds have inclusions and many of them are very cloudy indeed.

Peridot sun glasses would have been be far more useful, but aquamarine, which is also beryl, would have been absolutely perfect.

"Aquamarines"

Three aquamarines and an emerald

Unlike emerald, aquamarine occurs in large clear crystals in a range of pure light blues varying from relatively intense to very pale, as well as the bluish green variety mentioned above. It is certainly possible that the Romans made magnifying glasses out of aquamarine. Its first documented use was by the Greeks, who were wearing aquamarine amulets, engraved with the god Poseidon on a chariot, between 480-300 BC.

Lenses ground from aquamarine were also used as eyeglasses to correct shortsightedness in medieval Germany. The original word for these lenses was "brille", which is derived from the word beryl, and still in use today.

Several other blue gemstones occur in pale colours very similar to aquamarine and include some of the gems listed below.

"Sapphires"

Blue gemstones are even more confusing, since the word sapphire was originally used for all blue stones, including lapis lazuli and possibly turquoise too, while the stones we call sapphires today were often called blue rubies or hyacynths. Curiously only rare red zircons are called hyacynths today.

Sapphire, topaz, zircon, tourmaline, spinel, iolite and diamond

In some parts of Asia in antiquity, sapphires were regarded as unripe rubies. Burying them back in the ground was believed to ensure that they would eventually mature into rubies. These days any corundum which isn't a rich pure red is referred to as sapphire.

Blue sapphires may also be confused with the following gemstones:

Iolite, which meant violet in Greek, is a fascinating stone with unique optical properties. Legend has it that iolite was used as the world's first polarizing filter by the Vikings when they were too far from land to determine their position at sea. By looking through a lens made from iolite, they could determine the exact position of the sun and set an accurate course across the oceans.

The property that made iolite so valuable to navigators is an extreme pleochroism. Iolite has different colors in different directions within the crystal. A cube cut from this gemstone would look almost as blue as a sapphire from one side, as clear as water from the other and as yellow as honey from the top. It may be because of their value to sailors that they used to be called water sapphires.

"Pinks"

Pink gemstones can be particularly difficult to identify by eye and include:

"Amethysts"

Purple stones include:

The best amethysts, which come from Siberia, are a full rich velvety purple, which is almost red by artificial light and violet by daylight. Oriental amethyst (purple ruby) is redder in tone in daylight and almost ruby red in artificial light.

"Diamonds"

Stones which historically have been referred to as diamonds include:

Some of the legendary engraved diamonds of antiquity may have been phenakites.

"Foilbacks"

A foilback (or foiled stone) is a stone that has a metallic foil backing, often made of mercury and tin. Coloured foil is applied to the back of a stone to make the stone more reflective. Before cuts like the brilliant were invented, even precious stones were foiled to change their colour or enhance their sparkle. Moisture can damage the foil and make the stone look dull. Stones are rarely foiled any more but it used to be very common.

Other properties, which are unique to each variety of gemstone, are much more reliable than colour for identifying a particular gem.

Copyright©2005 Alex Murray.