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Natural Untreated Gemstones
|Pliny's Natural History|
The idea that the beauty of a gemstone could be improved through technical means is an ancient one. Indeed, gem treatments and enhancements are nearly as old as the history of gemstones. The earliest record is found in the Natural History of Pliny the Elder (23 to 79 AD), the encylopedic work which tried to collect much of the knowledge present at the time of the Roman Empire, especially in the fields of astronomy, zoology, botany, geology and mineralogy.
Based on the authorities of the time, Pliny discusses a range of techniques for enhancing gemstones, including heat treatment, dyeing, oiling, coating and the use of foil backings. We tend to think many of these techniques are recent inventions, but they were apparently known to gem experts more than 2,000 years ago.
Because fine gemstones are so rare, it is natural to try to maximize the beauty of any material found. Some gem enhancements were undoubtedly deceptive, and were deployed for illicit profit. The practice today is for all gem treatments to be disclosed to the consumer, and this is a rule that reputable dealers follow religiously, supported by professional gemological testing.
The most common gem treatment found today is heat treatment, which is applied routinely to sapphire and ruby, as well as to other gems such as blue zircon and tanzanite. Irradiation is widely used to create blue topaz from colorless topaz; indeed it's nearly impossible to buy a blue topaz which has not been enhanced through irradiation. Almost all emeralds are treated with oils or resins to fill tiny fractures, and more recently we've seen a new technique for fracture-filling low grade ruby with lead glass. Another new treatment for sapphire is known as lattice diffusion, which involves high temperature heating with beryllium to enhance the color.
For buyers who prefer to buy a completely untreated gemstone for an engagement ring or other special occasion, there are still a number of choices. You don't need to pay the very high prices for rare untreated sapphires or rubies in order to buy a fine untreated gem. There are still some gemstone varieties that combine superior hardness, brilliance and clarity with outstanding color, yet are never treated. You can buy these with confidence, knowing that you are buying a completely natural gem.
Spinel heads the list of gem varieties which are rarely, if ever, treated. Due to limited supply, natural spinel is rarely marketed in the jewelry business. But it is a great favorite of gem dealers and collectors for its excellent hardness (8 on the Mohs scale), brilliance and fire. It is available in a wide range of colors, including red, pink, orange, violet and blue. The rare neon pink-red spinel from Mahenge, Tanzania is one of the finest colored gems known.
Tsavorite Garnet is a vivid green gem found in Kenya and Tanzania. Known for its exceptional brilliance and fire, tsavorite is also more durable than emerald, with superior clarity. Most tsavorite is found in smaller sizes, with stones over 2 carats very uncommon.
Spessartite Garnet is another brilliant garnet, occurring in shades from orange-red to mandarin orange. Like all the garnets, spessartite is hard enough to be suitable for all kinds of jewelry, including rings. The rare pure orange spessartite from Nigeria is sought after by collectors.
Chrysoberyl is one of the hardest of all our colored gemstones, with a hardness rating of 8.5 on the Mohs scale, right below ruby and sapphire at 9. The most famous chyrsoberyls are the color-change alexandrite and chyrsoberyl cat's eye, but the greenish-golden chryoberyl is also very attractive. All the chyrsoberyl varieties are completely untreated.
Tourmaline offers a huge selection of colors, the most of any untreated gemstone. Tourmaline is also popular for its attractive luster and its unique bi-color stones, and can be found in larger sizes at affordable prices. Some tourmaline species, such as the rare rubellite and and paraiba varieties
There are other untreated varieties which are worth noting, including the black star sapphires from Thailand; all the rare garnet varieties such as demantoid, rhodolite and mali garnet; precious opal; and the olive-green peridot.