metamorphic
Epidote
Epidote - Ca2(Al,Fe)3(SiO4)3(OH)
Hardness: 6-7 Mohs; Color: Pistachio-green to yellowish-green; Luster: Vitreous; Crystal Structure: Monoclinic; Cleavage: Perfect in one direction; Specific Gravity: 3.3-3.6
- Hardness
- 6-7 Mohs
- Color
- Pistachio-green to yellowish-green
- Luster
- Vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Pistachio-green to yellowish-green; Luster: Vitreous; Crystal Structure: Monoclinic; Cleavage: Perfect in one direction; Specific Gravity: 3.3-3.6
Formation & geological history
Commonly formed in regional and contact metamorphic rocks such as greenschist and skarns, often resulting from the hydrothermal alteration of calcium-rich minerals like plagioclase feldspar.
Uses & applications
Primarily used as a semi-precious gemstone (Unakite) for jewelry, cabochons, and decorative carvings; also a significant indicator mineral for geologists identifying metamorphic facies.
Geological facts
The name comes from the Greek word 'epidosis', meaning 'addition', referring to the crystal's geometry where one side of the base is longer than the other. It is the defining mineral of the 'Epidote-amphibolite' metamorphic facies.
Field identification & locations
Identify in the field by its distinct 'pistachio' green color and its association with other metamorphic minerals like chlorite and actinolite. Often found in Alpine vents and metamorphic complexes.
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