Minerals (Category B)
Epidote is actually a group of closely related minerals, but in the gem trade, the name typically refers only to the gem-quality green variety of the mineral epidote. The name 'epidote' is derived from the Greek word for 'addition' which refers to its numerous crystal faces. Although rarely of gem-quality and especially rare as a faceted gemstone, epidote is a commonly occurring mineral.
Epidote is a complex form of calcium aluminum iron silicate in which both calcium and aluminum ions are replaced by other metals such as manganese, ferric iron or yttrium and cerium metals. Since epidote is an alteration product, it has a wide variance in composition and chemical formula. Depending on the exact levels of iron, manganese and other substances, stones may be classified under various trade names or in many cases, as their own distinct mineral.
Clinozoisite is a white to pink colored form of epidote with a low iron content, resulting in a very a similar chemical composition to zoisite. Zoisite is best known for its violet-blue form known as tanzanite. Piemontite is a red manganese epidote typically occurring in an opaque form. Tawmawite is a chromium-rich dark green variety of epidote mined from Burma. Unakite is an altered form of granite with characteristic inclusions of epidote, often used in cabochon jewelry.