metamorphic
Epidote
Epidote Group (Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH))
Hardness: 6-7 (Mohs scale); Color: Pistachio-green, yellowish-green to brownish-black; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 3.3–3.6
- Hardness
- 6-7 (Mohs scale)
- Color
- Pistachio-green, yellowish-green to brownish-black
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Pistachio-green, yellowish-green to brownish-black; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 3.3–3.6
Formation & geological history
Formed through regional or contact metamorphism of igneous rocks (like basalt or gabbro) or sedimentary rocks (like impure limestone). It often occurs in hydrothermal veins.
Uses & applications
Used primarily as low-cost gemstones (when transparent), in lapidary work for cabochons, and as a common specimen for mineral collectors. It is also an indicator mineral for metamorphic facies.
Geological facts
The name comes from the Greek word 'epidosis', meaning 'addition', referring to the crystal's geometry. Pistacite is a common name used for the pistachio-colored variety of epidote.
Field identification & locations
Identify in the field by its distinct 'pistachio green' color and its association with altered igneous rocks. Commonly found in locations like the Alps, Alaska, and Norway.
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