This is the blue variety of zoisite.
It would have been known since 1954, but it was in 1967 that Manuel de Souza “discovered” this gem by chance, in Arusha, Tanzania. Soon there were talks in the media about the “blue treasure of Africa”, referring to large crystals looking like sapphires. John Saul, a geologist working at the site, sent samples to his father in New York that brought them to the famous jeweler Tiffany’s who named it “tanzanite” because the English pronunciation of “zoisite” was too close to the word “suicide”. .. and launched it in the U.S. market in 1968. But according to some says, it was the vice president of a New York museum, Henry Pratt, who bought it by chance in 1968, in Idar-Oberstein (Germany). Researchers at the German study of gems of Idar Oberstein identify it as an unknown variety of zoisite. During its formation, it is the transformation of vanadium between 450 ° C and 700 ° C which gives it its blue color.
Tanzanite is not a mineral recognized by the International Mineralogical Commission, for which it is only zoisite, close to epidotes.
In the 1990s, some “tanzanite”samples, or rather, some colorless, green, orange-brown zoisites, were discovered, the green chromium variety was wrongly called “green tanzanite”.
Tanzanite has the characteristic of changing color according to light: blue under the light, it becomes violet under incandescent light.