What kind of garnet is tsavorite? If you look at a gemological reference you'll see that there are 6 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. But 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?
Though the name tsavorite looks like a gemological name, it is actually a marketing name. The name was proposed by Henry Platt, then 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 the source for the name tanzanite for blue zoisite.
Tsavorite is actually a variety of grossularite garnet, which is a 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 its 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 and much rarer than large emeralds. Miners estimate that 85% of the material mined yields gems under 1 carat, while 10% yields stone above one carat and only 2.5% yields stones over two carats, and 1% stones over 3 carats. Thus far 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 green/blue or green/yellow. You want to avoid gems that look like peridot (yellowish green) or stones that are too dark in tone (greenish black).
Tsavorite is 200x rarer than emerald, and is more brilliant due to a higher refractive index (1.74 vs. 1.596). 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.