metamorphic
Epidote
Calcium aluminum iron silicate hydroxide (Ca2(Al,Fe)3(SiO4)3(OH))
Hardness: 6-7 Mohs; Color: Pistachio green to dark green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 3.3 to 3.5.
- Hardness
- 6-7 Mohs
- Color
- Pistachio green to dark green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 Mohs; Color: Pistachio green to dark green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 3.3 to 3.5.
Formation & geological history
Formed under low-to-medium grade regional metamorphism of igneous rocks like basalt. It also occurs in hydrothermal veins and contact metamorphic zones (skarns).
Uses & applications
Used primarily as a semi-precious gemstone when transparent, as an ornamental stone, and as a common indicator mineral for geologists studying metamorphic conditions.
Geological facts
The name comes from the Greek word 'epidosis', meaning 'addition', referring to its crystal geometry. Its distinctive 'pistachio' color is one of the most reliable identification features in geology.
Field identification & locations
Identify in the field by its unique yellow-green color (pistachio green) and its occurrence in association with minerals like chlorite or actinolite. Common in mountain belts and volcanic terrains.
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