Zoisite Gemstones

The mineral zoisite was first discovered by the mineral dealer Simon Prešern, who discovered it in the Saualpe mountains of Austria in 1805. He brought a sample to the Slovene mineralogist Sigmund Zois (1747-1819), who recognized it as a previously unknown mineral. It was first named Saualpite, after its location, then named Zoisite in honor of Baron Zois.

It sounds like just another story about the discovery of an obscure mineral. But zoisite turned out to be an important gemstone mineral when a new variety of zoisite was discovered in Tanzania in 1967. That find eventually led to the marketing of one of the most popular gemstones of our time, tanzanite.

Natural Thulite

There are in fact three gemstone members of the zoisite species: tanzanite, thulite and anyolite. By chemical composition, zoisite is a calcium aluminum silicate with a hardness of 6.5 to 7 on the Mohs scale. When found in distinct crystals (rather than in massive form) it has quite a high refractive index, just slightly lower than spinel.

Tanzanite, still found only in its first location in Tanzania, is very well-known, but thulite and anyolite are not. Thulite is an opaque, massive manganese-rich variety of zoisite that is pink in color. It was first discovered in Norway in 1820 and named after the mythical island of Thule. Thulite is usually cut as cabochons or for carving ornamental objects. Since the first find in Norway, deposits have also been found in Western Australia, Namibia and North Carolina in the USA.

Anyolite was first discovered near Longido in Tanzania in 1954. Though considered a variety of zoisite, strictly speaking it is a metamorphic rock composed of intergrown green zoisite, black hornblende and ruby. Sometimes it is called Ruby-Zoisite, since its chief attraction is the interesting contrast of green zoisite and red ruby. The name Anyolite apparently comes from the Masai anyoli, meaning "green."

Anyolite or Ruby-Zoisite is generally used for carving ornamental objects. The variable amount of ruby in this material is opaque and of low quality, so there is no attempt to extract the ruby from it. Tanzania continues to be the main producer of Anyolite, where it is mined in appreciable quantities for gem carvers and collectors.

The story of the discovery and marketing of tanzanite is fascinating enough to deserve its own treatment. Please see our articles on Discovery of Tanzanite and Tanzanite Prices.