metamorphic
Epidotite (Unakite-related Epidote)
Epidote (Ca2(Al2,Fe)(SiO4)(Si2O7)O(OH))
Hardness: 6-7 on Mohs scale. Color: Pistachio-green to yellowish-green. Luster: Vitreous to pearly. Crystal structure: Monoclinic (though typically massive in rock form). Cleavage: Perfect in one direction. Specific Gravity: 3.3 to 3.5.
- Hardness
- 6-7 on Mohs scale
- Color
- Pistachio-green to yellowish-green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Pistachio-green to yellowish-green. Luster: Vitreous to pearly. Crystal structure: Monoclinic (though typically massive in rock form). Cleavage: Perfect in one direction. Specific Gravity: 3.3 to 3.5.
Formation & geological history
Formed through hydrothermal alteration of primary minerals like feldspars, pyroxenes, or amphiboles during low-grade regional or contact metamorphism. Often found in altered igneous rocks.
Uses & applications
Used primarily as decorative stone, lapidary material for cabochons and beads, and as an indicator mineral for geologists tracking metamorphic grades.
Geological facts
The distinctive 'pistachio' color is caused by the presence of iron (Fe3+). It is the namesake mineral for the 'epidote facies' of metamorphic rocks, indicating specific temperature and pressure conditions during formation.
Field identification & locations
Identify in the field by its unique yellow-green color (resembling a Granny Smith apple or pistachio) and its hardness, which allows it to scratch glass. Commonly found in subduction zones or greenstone belts.
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