metamorphic
Epidosite (Epidote-rich rock)
Epidotalite (primarily Ca2(Al2Fe3+)(SiO4)(Si2O7)O(OH))
Hardness: 6-7 on Mohs scale; Color: Pistachio-green to yellowish-green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; 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; Cleavage: Perfect in one direction; Specific gravity: 3.3 to 3.5.
Formation & geological history
Formed through hydrothermal alteration of mafic igneous rocks (saussuritization) or regional metamorphism of calcium-rich rocks. It is commonly found in basaltic rocks that have undergone low to medium-grade metamorphism.
Uses & applications
Used primarily as a decorative stone and for architectural veneers. It is popular among mineral collectors. High-quality transparent crystals are occasionally faceted as gemstones (Pistacite).
Geological facts
Epidote gets its name from the Greek word 'epidosis' (addition), referring to one side of the ideal prism being longer than the other. It is a key indicator mineral for the greenschist metamorphic facies.
Field identification & locations
Identify in the field by its distinctive 'pistachio green' color and its association with quartz and chlorite. It is commonly found in the French Alps, Norway, and the Blue Ridge Mountains of the USA. Collectors look for its granular or columnar crystalline mass.
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