metamorphic
Epidosite (Unakite-related)
Epidosite (predominantly Epidote, Ca2(Al2,Fe3+)(SiO4)3(OH))
Hardness: 6-7 Mohs; Color: Pistachio green to dark olive; Luster: Vitreous to greasy; Crystal Structure: Monoclinic; Specific Gravity: 3.3-3.6; Smooth texture when water-worn.
- Hardness
- 6-7 Mohs
- Color
- Pistachio green to dark olive
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 6-7 Mohs; Color: Pistachio green to dark olive; Luster: Vitreous to greasy; Crystal Structure: Monoclinic; Specific Gravity: 3.3-3.6; Smooth texture when water-worn.
Formation & geological history
Formed via hydrothermal alteration of mafic igneous rocks (hydrothermal metamorphism). Often found in areas of tectonic activity where basalt or gabbro has been chemically altered by hot, mineral-rich fluids.
Uses & applications
Used primarily as decorative stone, in lapidary work for cabochons and beads, and as architectural stone if found in large enough quantities.
Geological facts
Epidosite is closely related to Unakite, but lacks the pink orthoclase feldspar that characterizes true Unakite. The name comes from the Greek word 'epidosis', meaning 'addition', referring to the increase in crystal face development.
Field identification & locations
Identify by its distinct 'pistachio' green color and hardness (it will not be scratched by a steel knife). Commonly found in riverbeds and glacial tills in the Appalachian Mountains and Lake Superior regions.
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