African Tsavorite Gemstones
What kind of garnet is tsavorite? If you look at gemological information, you'll see that there are six kinds of garnet; pyrope, almandite, spessartite, grossularite, andradite and uvarovite. All of these have a similar crystal structure, but they vary slightly in their chemical composition. One name you won't find on the list is tsavorite, though it is one of the most famous and expensive garnets. What happened to tsavorite?
African Tsavorite Garnet
Though the name tsavorite looks like a gemological name, it is actually a marketing name. The name was proposed by Henry Platt, who was president of Tiffany & Co. when the gem was first first discovered in East Africa in 1967. The name is derived from Tsavo National Park in Kenya. Platt, a great-grandson of Louis Comfort Tiffany, was also responsible for the name tanzanite that was attributed to blue zoisite.
Tsavorite is a variety of grossularite garnet, which is composed of calcium aluminum silicate. The other varieties are hydrogrossular (green), leuco garnet (colorless) and hessonite (brown-red). What is special about tsavorite is that it is colored by trace amounts of chromium or vanadium, giving it that distinctive emerald-like green. Its vivid color and extreme rarity caused a lot of excitement in the gem world, helped along by some promotion from Tiffany & Co.
Tsavorite was a very recent discovery. The first samples were found in 1967 by Campbell Bridges, a British geologist who was doing consulting work for Tiffany & Co. on the original tanzanite deposit in Tanzania.
The first tsavorite deposits across the border in Kenya were discovered by Bridges in 1970.
Large tsavorites are extremely rare; even rarer than large emeralds. Miners estimate that 85% of the material mined yields gems under 1 carat, while 10% yields stones above one carat and only 2.5% yields stones over two carats. Moreover, approximately 1% yields stones over 3 carats. To date, tsavorite deposits have only been found in Kenya and Tanzania in East Africa, and more recently (1991) in Madagascar.
When buying tsavorite, look for an intense vibrant green color. Like emerald, tsavorite can be bluish-green or yellowish-green. Gems that look like peridot (yellowish-green) or stones that are too dark in tone (greenish-black) should be avoided.
Tsavorite is rarer than emerald, and is more brilliant due to a higher refractive index (tsavorite has a refractive index of 1.74 to 1.759 whereas the refractive index of emerald is 1.602 at the most). Tsavorite is also a more durable gemstone. Where virtually all emeralds are treated with oils or resins to fill internal fractures, tsavorite is always untreated.