Taaffeite (pronounced TAR-fite) is one of the rarer gemstones known, and you'll often it see on lists of the most exotic stones in the world, along with esoteric minerals such as painite, musgravite and grandidierite.
Taaffeite was first discovered in 1945 by the Irish-Austrian gemologist, Count Edward Charles Richard Taaffe (1898 - 1967). Taaffe was sorting through a parcel of cut and polished Sri Lankan spinel gemstones when he discovered something that he knew could not be spinel since it was so obviously doubly refractive (spinel, like garnet and diamond, is singly refractive). This is one of the rare cases where the first sample of a new gem variety was found in the form of a faceted stone.
Apart from being doubly refractive, taaffeite has many similarities to spinel. It is very hard, with a Mohs hardness rating of 8 to 8.5, whereas spinel has a score of 8. Taaffeite has a specific gravity of 3.60 to 3.62, almost identical to that of spinel (3.54 to 3.63); and a refractive index of 1.719 to 1.730, also similar to spinel, which has a refractive index of 1.712 to 1.762. By chemical composition, taaffeite is magnesium beryllium aluminum oxide (whereas spinel is magnesium aluminum oxide). The most common inclusions in taaffeite are apatite and zircon crystals.
Taaffeite Rough Stone
Taaffeite is known to be colorless, violet, red, green or blue. The most common colors are fairly unsaturated mauve and lavender. Deeper red and purple, colored by traces of chromium and iron, is extremely rare. The largest taaffeite to reach the market was a 33-carat stone sold at a Hong Kong auction in 1999.
Most taaffeite has been misidentified as spinel. But as awareness of its differences to spinel grows, more taaffeite is being discovered. To date, Sri Lanka and Tanzania appear to be the only sources for this material. However, because of the geological connection between the deposits in Sri Lanka, Madagascar and East Africa, gemologists expect that taaffeite will eventually be discovered in Madagascar as well.