Precious gemstone zoisite was named for the Slovenian noble, Sigmund Zois (1747-1819), Baron of Edelstein, who financed mineral-collecting expeditions. This mineral was found in 1805 on the Saualpe Mountains, Austria, and was originally called saualpite. In 1967, a blue-to-violet transparent variety was discovered in Tanzania, near Mount Kilimanjaro. Beside Tanzania, USA (North Carolina), Australia, and Pakistan are also the main sources. This variety was given the name tanzanite. A pink variety called thulite (named after the ancient name for Norway, where it was found) is usually massive. Anyolite is the name frequently applied to gem material that consists largely of massive, apple-green precious gemstone zoisite with bright red corundum. Colors available are blue-to-violet (tanzanite), pink (thulite), yellowish brown, gray, and greenish.
Precious gemstone zoisite is coming from the class of silicates with paired silica tetrahedra. The dispersion is about 0.018-0.020 and the specific gravity comes in 3.10-3.38 range. It is composed from calcium aluminium silicate hydroxide. precious gemstone zoisites has a orthorhombic system and its habit is prismatic crystals, often with complex terminations. The birefringence of precious gemstone zoisite is 0.009 and the hardness stopped at level 6. Transparent material is fashioned into natural gemstones (usually in a step cut); jewelers prefer to call transparent precious gemstone zoisite of any color tanzanite, as this word is more familiar to the public. Translucent to opaque anyolite is usually carved into sculptures and other works of art. Precious gemstone zoisite is also cut en cabochon and in cameos. In gem varieties precious gemstone zoisite’s refractive index is in 1.692-1.702 range. Tanzanite is brittle and should not be worn as a ring stone on a daily basis.
Precious gemstone zoisite has a complex composition, containing both single silicate tetrahedra and paired tetrahedron groups. Its cleavage is perfect in one direction. It occurs as prismatic, orthorhombic crystals, or in massive form, and is found in metamorphic and pegmatitic rock. The luster of precious gemstone zoisites is vitreous to pearly and the fracture is even. Most purple and blue tanzanites are the result of heat treatment. The rough is a yellowish brown color when it is mined, but turns violet-blue when heated. Tanzanite owes its color to vanadium. Some transparent green stones contain both vanadium and chromium. The pink color of thulite is due to the presence of manganese. Green and pink pure massive precious gemstone zoisites have been used as a substitute for jade.
