Zoislite

Zoislite is a mineral belonging to the epidote group. It is an aluminum iron calcium silicate mineral with the chemical formula Ca2Al3(SiO4)(Si2O7)O(OH). Zoislite typically forms in metamorphic rocks, often appearing in greenschist and amphibolite facies. It can also be found in some igneous rocks.

The mineral commonly occurs as prismatic crystals, but it can also be found in granular or massive forms. Its color varies widely, ranging from colorless and gray to green, brown, and black. Some varieties of zoislite exhibit pleochroism, meaning they display different colors when viewed from different angles.

A notable variety of zoislite is tanzanite, which is a deep blue to violet gemstone. Tanzanite is only found in one location in the world, the Merelani Hills in Tanzania, making it a relatively rare and valuable gemstone. Other attractive forms of zoislite, such as the "ruby zoislite" which contains red ruby inclusions, are also used for ornamental purposes and in jewelry.

Zoislite was first discovered in the Saualpe mountains of Carinthia, Austria, and was named in honor of Sigmund Zois, Baron von Edelstein. While zoislite itself is not particularly rare, certain colored varieties and gem-quality specimens are highly sought after.