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À propos des pierres précieuses non-traités
Untreated Gemstones

It's a fact of life in the gemstone industry that many gems are treated. The most common form of treatment is heat treatment, which is applied routinely to ruby and sapphire, and to other gems such as tanzanite, blue zircon and blue apatite. Some gems, such as blue topaz, are irradiated to produce their distinctive color; in fact it's virtually impossible to buy a blue topaz which has not been irradiated. Other gems, such as emerald, are treated with oils or resins to fill fractures. More recently, we've seen heat treatment with beryllium diffusion for yellow and orange sapphires, and fracture-filling with lead glass for African rubies. Sometimes it seems like the gem world is awash in gem treatments.

The idea of treating gems is hardly new. Pliny's Natural History, the compendium of knowledge from ancient Rome written in the first century A.D., discusses a range of techniques for altering gems, including heating, oiling, dyeing and the use of foil backings and coatings. Some of those ancient techniques were undoubtedly deceptive, but today gem treatments are just a way for the industry to meet world demand for gemstones in the face of very limited supply.

Despite the proliferation of gem treatments, there are still many choices for buyers who insist on an untreated gem. You don't need to pay a fortune for very rare untreated sapphires or rubies. There are a number of gemstone varieties that combine good gemstone characteristics -- hardness, durability, brilliance and clarity -- with outstanding color, yet are never treated. You can buy these with confidence, knowing you are buying a completely natural gem. Here are our recommendations for untreated gem varieties:

Spinel
Natural Untreated Spinel In the view of many gem dealers, spinel is the finest untreated gem variety available in today's market. With a hardness of 8 on the Mohs scale, and excellent clarity and dispersion (fire), spinel has often been confused with ruby and sapphire. A good range of colors are available, including red, orange, violet, blue, pink, green and silver.
Spessartite Garnet
Untreated Spessartite Garnet Spessartite's mandarin orange and orange-red colors are unique in the gemstone world. Spessartite has a higher refractive index than sapphire, so it has superb brilliance. With a hardness of 7 to 7.5 on the Mohs scale, spessartite is hard enough for rings.
Rhodolite Garnet
Natural Untreated Rhodolite Garnet A mixture of pyrope and almandite garnet, rhodolite is a rose-red to purple-red garnet with none of the brownish tones associated with common red garnet. With the good hardness, brilliance and clarity of garnet, this is a red gem suitable for all kinds of jewelry.
Tsavorite Garnet
Untreated Tsavorite Garnet Colored by chromium and/or vanadium, fine examples of tsavorite rival emerald for intensity of green. But tsavorite has better clarity and durability than emerald, and it is never treated. Due to its rarity, tsavorite is difficult to find in larger sizes.
Tourmaline
Fine Natural Tourmaline Tourmaline provides the greatest selection of colors in any untreated gemstone. In addition to its vitreous luster and excellent clarity, tourmaline can often be found in larger sizes at affordable prices. It has become our best-selling gemstone.
Peridot
Natural Untreated Peridot Peridot is one of the idiochromatic gems, meaning its color derives from its basic chemical composition, not from trace impurities. So that means it only occurs in shades of green. It also means its color cannot be modified by any form of treatment.
Orange, Brown and Rose Zircon
Rare Untreated Pink Rose Zircon While the popular blue zircon is heat treated, there are natural colors of zircon which are not treated in any way. These include brown, rose, rose-orange and golden orange hues. Note that the yellow and white zircon is almost always heat treated. Zircon is valued especially for its brilliance and fire. It has a refractive index higher than sapphire and spessartite garnet, and its dispersion or fire is nearly as pronounced as diamond.
  • First Published: March-28-2008
  • Last Updated: March-01-2011
  • © 2005-2014 GemSelect.com all rights reserved.
    Reproduction (text or graphics) without the express written consent of GemSelect.com (SETT Company Ltd.) is strictly prohibited.
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