metamorphic
Epidosite
Epidosite (composed primarily of Epidote and Quartz)
Hardness: 6-7 (Mohs scale); Color: pistachio green, olive green, or yellow-green mixed with white/grey quartz; Luster: vitreous to pearly; Crystal structure: Monoclinic (Epidote component); Specific gravity: 3.2-3.5.
- Hardness
- 6-7 (Mohs scale)
- Luster
- vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs scale); Color: pistachio green, olive green, or yellow-green mixed with white/grey quartz; Luster: vitreous to pearly; Crystal structure: Monoclinic (Epidote component); Specific gravity: 3.2-3.5.
Formation & geological history
Epidosite is a hydrothermally altered metamorphic rock. It forms when mafic igneous rocks (like basalt) undergo metasomatism, where hot, mineral-rich fluids transform plagioclase and pyroxene into epidote and quartz. Typically associated with Ophiolite complexes.
Uses & applications
Used primarily as a decorative stone, in lapidary work for cabochons and tumbled stones, and as an indicator mineral for geologists searching for hydrothermal ore deposits (like copper).
Geological facts
The distinctive pistachio-green color is caused by the presence of iron in the epidote crystal structure. It is often found in the 'sheeted dike' sections of ancient oceanic crust that have been pushed onto land.
Field identification & locations
Identify in the field by its characteristic pale 'pistachio' green color and its hardness (it will scratch glass but not quartz). Commonly found in creek beds near metamorphic belts, especially in the Appalachian Mountains or Pacific Coast ranges.
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