|Epidote and Unakite
Epidote is a silicate mineral that is often recognized by its pistachio green color. Once known as pistacite for its color, the accepted mineralogical name is epidote, named after its numerous crystal faces (from the Greek for "addition"). Transparent dark green crystals have been cut as gemstones, and somewhat resemble diopside, dravite tourmaline or idocrase.
By chemical composition, epidote is a 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 varying angles. Epidote has a high refractive index (1.729-1.768), similar to pyrope garnet, and it has a bright vitreous luster when polished.
Epidote is actually a family of related minerals, since there are some variations in the chemical composition. Clinozoisite is a a white or pink epidote that is low in iron, giving it a similar chemical composition to zoisite. Piemontite is a a red opaque epidote containing manganese, while Tawmawite is a dark green chromium-bearing epidote from Burma.
Deposits of epidote are found in many locations, including Sri Lanka, Burma, Brazil, Mozambique, Kenya, Mexico, Austria, Norway and the USA.
Epidote is also a key component of some rocks. Epidosite is a rock composed of quartz and epidote. Unakite is an 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 carved into decorative objects.
Unakite is found in several locations in the United States as well as in Brazil, South Africa and Sierra Leone.
- First Published: July-15-2010
- Last Updated: October-07-2010
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