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By Reviewed By Andreas Zabczyk Jul 15, 2010 Updated Aug 15, 2017

Epidote and Unakite

Epidote Crystals
Epidote Crystals

Epidote is a silicate mineral that is often recognized by its pistachio green color. It was once known as pistacite because of its color, but the accepted mineralogical name is epidote, which comes from the Greek for "addition", due to its numerous crystal faces. Transparent dark-green crystals have been cut as gemstones and somewhat resemble chrome diopside, chrome dravite tourmaline or idocrase (vesuvianite).

By chemical composition, epidote is calcium aluminum iron silicate. It has a hardness of 6 to 7 on the Mohs scale. One of its distinguishing characteristics is strong pleochroism, where crystals display different colors - green, brown and yellow - as they are viewed from different angles. Epidote has a high refractive index (1.729 to 1.768), similar to that of pyrope garnet, and it has a bright vitreous luster when polished.

Pistachio Green Epidote Rough
Pistachio Green Epidote Rough

Epidote is actually a family of related minerals, which show some variations in their chemical composition. Clinozoisite is white or pink epidote that is low in iron, giving it a similar chemical composition to zoisite. Piemontite is opaque and red variety of epidote containing manganese, while tawmawite is dark-green chromium-bearing epidote from Burma.

Deposits of epidote are found in many locations, including Sri Lanka (Ceylon), Myanmar (Burma), Brazil, Mozambique, Kenya, Mexico, Austria, Norway and the USA.

Tumbled Unakite
Tumbled Unakite

Epidote is also a key component of some rocks. Epidosite is rock composed of quartz and epidote. Unakite is altered granite that is composed of epidote, pink orthoclase feldspar and colorless quartz. It is named after the Unakas Mountains of North Carolina in the United States, where it was first discovered. Good quality unakite takes a good polish and is often used to produce cabochons for jewelry or shaped into decorative ornamental gemstone carvings and various objects.

Unakite is found in several parts of the United States, and also in Brazil, South Africa and Sierra Leone.

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