Tsavorite

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Tsavorite
Graphite-Grossular-Strontiumapatite-d06-195a.jpg
Tsavorite garnet on real matrix of silvery black graphite and a minor blue apatite
General
CategoryNesosilicate
Formula
(repeating unit)
Ca3Al2Si3O12
Crystal systemcubic
Identification
ColorLight to deep green
Mohs scale hardness7 – 7.5[1]
Specific gravity3.60–3.68[1]
Optical propertiesSingle refractive
Refractive index1.740[1]
Dispersion0.028[1]

Tsavorite or tsavolite is a variety of the garnet group species grossular, a calcium-aluminium garnet with the formula Ca3Al2Si3O12.[2] 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[3] 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.

Peter Morgan, founder of Eltons Mining Ltd. and his team were the first to discover commercially viable quantities of the gem, near the Tsavo West National Park. They then formed a group of overseas scientists and dealers to evaluate the gem and advise on how best to market it; these included two eminent mineral scientists, Prof. Dr. Edward Gubelin from Switzerland and Prof. Dr. Herman Bank from Germany, plus other stalwarts of the gemstone industry. Peter came into the mining industry after he and a partner bought Nairobi's leading jewellers, Elton's Jewellers Ltd.

In the presence of some members of this group, Peter Morgan suggested the name Tsavolite; the first part derives from the district in the Taita Taveta province where the gem was discovered; the -lite suffix simply refers to the Greek word for stone.

Campbell Bridges also 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. Peter Morgan and Dan Meyer introduced the gem to Harry Platt, the then vice-president of New York jewellers Tiffany & Co., who was keen to market Tsavolite. Unfortunately, the proposed terms and conditions were unacceptable, so the partnership never materialised. However, Harry Platt wrote a complimentary article for the Lapidary Journal, in which he claimed the name Tsavorite, he subsequently insisted that ‘came off the American tongue better’. And so the new name stuck.[3]

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.[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 yet been discovered.[5]

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.[6]

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.[7]

References[edit]

  1. ^ a b c d 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
  2. ^ Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  3. ^ a b Idar-Oberstein, Tsavorite Archived 2008-06-10 at the Wayback Machine International Colored Gemstone Association, accessed online January 24, 2007
  4. ^ http://news.bbc.co.uk/2/hi/uk_news/8198630.stm BBC News 13 August 2009 Mob kills UK gems expert in Kenya
  5. ^ Tsavorite Garnet Value, Price, and Jewelry Information International Gem Society - Tsavorite Garnet Value, Price, and Jewelry Information - Accessed online February 18th, 2016
  6. ^ 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
  7. ^ Common and Uncommon Inclusions Found in Tsavorite Lapigems Ltd, - Common and Uncommon Inclusions Found in Tsavorite - Accessed online November 2nd, 2016

External links[edit]