Tsavorite
| Tsavorite | |
|---|---|
| General | |
| Category | Mineral |
| Formula (repeating unit) | Ca3Al2Si3O12 |
| Crystal system | cubic |
| Identification | |
| Color | Light to deep green |
| Mohs scale hardness | 7 - 7.5 [1] |
| Specific gravity | 3.60–3.68 [1] |
| Optical properties | Single refractive |
| Refractive index | 1.740[1] |
| Dispersion | 0.028 [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.
Green grossular had been rare until 1967, when a British gem prospector and geologist Campbell R. Bridges came across a deposit of the mineral in the mountains of north-east Tanzania.[3] 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 gelogoical 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. He was granted permit registration to mine the deposit. Until 1974, the gemstone was only known to mineral specialists. In that year Tiffany and Co launched a marketing campaign which brought broader recognition of the stone.[3]
The name tsavorite was proposed by Tiffany and Co president Henry Platt in honor of Tsavo National Park in Kenya.[3] 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 clean gems over 1 carat (200 mg) in weight, tsavorite has been found in sizes yielding up to 15 carat (3 g) stones.
Recently, a gem quality tsavorite likely to be the largest ever discovered, over 325 carats (65 g), became available in Thailand (see "Multicolour.com" external link below).
References
- ^ 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
- ^ Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN:0-87311-019-6
- ^ a b c Idar-Oberstein, Tsavorite International Colored Gemstone Association, accessed online January 24, 2007