metamorphic
Epidote (with Quartz and Feldspar)
Epidote (unakalite/unite), Ca2(Al2Fe3+)(SiO4)(Si2O7)O(OH)
Hardness: 6.0-7.0 on Mohs scale. Color: Pistachio green to dark olive green, often mottled with pink or gray. Luster: Vitreous to resinous. Crystal Structure: Monoclinic. Cleavage: Perfect in one direction. Specific Gravity: 3.3-3.6.
- Hardness
- 6
- Luster
- Vitreous to resinous
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Physical properties
Hardness: 6.0-7.0 on Mohs scale. Color: Pistachio green to dark olive green, often mottled with pink or gray. Luster: Vitreous to resinous. Crystal Structure: Monoclinic. Cleavage: Perfect in one direction. Specific Gravity: 3.3-3.6.
Formation & geological history
Formed through hydrothermal metamorphism or regional metamorphism of igneous rocks rich in calcium and aluminum. Often occurs in veins or as a secondary mineral in altered granite or basalt.
Uses & applications
Mostly used for jewelry (beads, cabochons), carvings, and as a collector's specimen. It is also used as a decorative stone in construction when found in large unakite blocks.
Geological facts
The name comes from the Greek word 'epidosis' meaning 'addition', referring to the crystal's geometry. Pistacite is a common name for the green variety because its color resembles pistachio nuts.
Field identification & locations
Identified by its distinctive yellowish-green 'pistachio' color and association with pink orthoclase feldspar. Look for it in areas of metamorphic activity or downstream in riverbeds as water-rounded pebbles.
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