Tsavorite

Tsavorite

Gem-quality Tsavorite from Tanzania, 0.9 x 0.7 x 0.4 cm.[1]
General
Category Mineral
Formula
(repeating unit)		 Ca3Al2Si3O12
Crystal system cubic
Identification
Color Light to deep green
Mohs scale hardness 7 – 7.5[2]
Specific gravity 3.60–3.68[2]
Optical properties Single refractive
Refractive index 1.740[2]
Dispersion 0.028[2]

Tsavorite or tsavolite is a variety of the garnet group species grossular, a calcium-aluminium garnet with the formula Ca3Al2Si3O12.[3] Trace amounts of vanadium or chromium provide the green color.

In 1967, British gem prospector and geologist Campbell R. Bridges discovered a deposit of green grossular in the mountains of north-east Tanzania[4] in a place called Lemshuko, 15 km (9.3 mi) away from Komolo, the first village. The specimens he found were of very intense color and of high transparency. The find interested the gem trade, and attempts were made to export the stones, but the Tanzanian government did not provide permits.

Believing that the deposit was a part of a larger geological structure extending possibly into Kenya, Bridges began prospecting in that nation. He was successful a second time in 1971, when he found the mineral variety there, and was granted a permit to mine the deposit. The gemstone was known only to mineral specialists until 1974, when Tiffany and Co launched a marketing campaign which brought broader recognition of the stone.[4]

Bridges was murdered in 2009 when a mob attacked him and his son on their property in Tsavo East National Park. It is believed that the attack was connected to a three-year dispute over access and control of Bridges' gemstone mines.[5]

The name tsavorite was proposed by Tiffany and Co president Sir Henry Platt in honor of Tsavo East National Park in Kenya.[4] Apart from the source locality in Tanzania it is also found in Toliara (Tuléar) Province, Madagascar. Small deposits of gem grade material have been found in Pakistan and Queen Maud Land, Antarctica. No other occurrences of gem material have been discovered.[6]

Rare in gem-quality over several carats (1 carat = 200 mg), tsavorite has been found in larger sizes. In late 2006 a 925-carat (185.0 g) crystal was discovered. It yielded an oval mixed-cut 325 carat (65 g) stone, one of the largest, if not the largest faceted tsavorites in the world. A crystal that yielded a 120.68-carat (24.136 g) oval mixed-cut gem was also uncovered in early 2006.[7]

Tsavorite formed in a Neoproterozoic metamorphic event which involved extensive folding and refolding of rock. This resulted in a wide range of inclusions forming within most Tsavorite crystals. These inclusions are strong identifying features in Tsavorite. [8]

See also

References

  1. ↑ Merelani Hills, Arusha Region, Tanzania from Mindat.org
  2. 1 2 3 4 Bancroft, Peter Tsavorite online reprint from Peter Bancroft’s classic book, Gem and Crystal Treasures (1984) Western Enterprises/Mineralogical Record, Fallbrook, CA, 488 pp., accessed online January 24, 2007
  3. ↑ Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  4. 1 2 3 Idar-Oberstein, Tsavorite International Colored Gemstone Association, accessed online January 24, 2007
  5. ↑ http://news.bbc.co.uk/2/hi/uk_news/8198630.stm BBC News 13 August 2009 Mob kills UK gems expert in Kenya
  6. ↑ Tsavorite Garnet Value, Price, and Jewelry Information International Gem Society - Tsavorite Garnet Value, Price, and Jewelry Information - Accessed online February 18th, 2016
  7. ↑ Giant size top color clean tsavorite discovered in East Africa Multicolour Gems Ltd, - Giant size top color clean tsavorite discovered in East Africa - Accessed online December 7th, 2009
  8. ↑ Common and Uncommon Inclusions Found in Tsavorite Lapigems Ltd, - Common and Uncommon Inclusions Found in Tsavorite - Accessed online November 2nd, 2016
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