Tsavorite

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

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

In 1967, British gem prospector and geologist Dr. Campbell R. Bridges discovered a deposit of green grossular in the mountains of north-east Tanzania in a place called Lemshuko, 15 km 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.

Dr. 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.

The name tsavorite was proposed by Tiffany and Co president Sir Henry Platt in honor of Tsavo East National Park in Kenya. Apart from the source locality in Tanzania it is also found in Toliara (Tuléar) Province, Madagascar, but so far, no other occurrences of gem material have been discovered.

Rare in gem-quality over several carats (1 carat = 200 mg) in weight, 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.

See also

• garnet
• almandine
• andradite
• grossular
• Siberian emeralds
• pyrope
• spessartine
• uvarovite
• geology
• mineral collecting
• mineral
• gemstone

External links

• Mindat.org
• http://www.gemstone.org/gem-by-gem/english/tsavorite.html The ICA's tsavorite information page.
• Machete mob murders British gemstone miner in Kenya (Campbell R. Bridges)
• Campbell Bridges - Daily Telegraph obituary