Vast ruby deposits were discovered in 1949 at Longido in northeast Tanzania at the foot of Mt. Kilimanjaro. The discovery was made by Tom Blevins, an English prospector. He thought he had made the find of the century and he and his partner would become immensely wealthy. It was not to be.
Though the ruby at Longido was found in astonishing quantity -- literally millions of carats -- much of it was coarse and opaque and encased in a green matrix that turned out to be the mineral zoisite.
It took some years before a market could be found for this material. In fact Blevins had given up trying to market it and had stored tons of it in his garage. He and his partner had turned their attention to meerschaum mining and pipe-carving instead.
While it was was not fine ruby, this material eventually found its uses in carvings, ornamental objects and cabochons. The combination of the green zoisite with its black streaks of hornblende, and the rich red and pink ruby is unique and attractive. It is one of the most colorful ornamental stones found in the world and the abundance of the material makes it very affordable, even in larger sizes.
The mineralogical name of ruby-zoisite is anyolite, said to be derived from the Masai word for green ("anyoli"). But it is most commonly called ruby-zoisite or ruby-in-zoisite. You may also hear it referred to as Tanganyika artstone.
The mineral zoisite was named after the Slovene mineralogist Sigmund Zois (1747-1819), who first recognized it as an unknown mineral when it was first discovered in the Austrian Alps in 1805. The other members of the zoisite family are thulite, an opaque, massive manganese-rich variety of pink zoisite that is pink in color; and tanzanite, the now famous violet blue gem produced by heat treatment of brown zoisite.
Ruby-zoisite rocks are difficult to fashion because of marked differences of hardness of their chief constituents. Zoisite and hornblende have a hardness of about 6.5 on the Mohs scale whereas ruby has a hardness of 9. Usually cutters try to emphasize the ruby portions of the material or achieve interesting contrasts.
Ruby-zoisite carvings are very popular, and the material is particularly well-suited for figures like turtles. Large cabochons make attractive pendants and recently we have seen some nicely polished faceted pieces that are very attractive.
The Longido mining district in Tanzania continues to be the sole source for the world's supply of ruby-zoisite.