metamorphic
Greenstone / Epidosite
Epidosite (Metasomatic rock consisting mainly of Epidite Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH) and Quartz)
Hardness: 6-7 on Mohs scale. Color: Pistachio green to dark olive. Luster: Vitreous to dull. Crystal structure: Monoclinic (microcrystalline). Cleavage: Perfect in one direction but rarely visible in massive form. Specific gravity: 3.2-3.5.
- Hardness
- 6-7 on Mohs scale
- Color
- Pistachio green to dark olive
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Pistachio green to dark olive. Luster: Vitreous to dull. Crystal structure: Monoclinic (microcrystalline). Cleavage: Perfect in one direction but rarely visible in massive form. Specific gravity: 3.2-3.5.
Formation & geological history
Formed through the hydro-thermal alteration (metasomatism) of mafic igneous rocks like basalt. It often occurs in greenschist facies metamorphic belts, frequently associated with seafloor spreading centers and subduction zones.
Uses & applications
Used primarily as decorative stone, aquarium gravel, or lapidary material for cabochons. Historically used for making stone tools due to its toughness and ability to hold an edge.
Geological facts
The term 'Greenstone' was used by early archaeologists to describe many dark green, tough lithic materials. Epidote, the primary green mineral, often indicates the presence of copper mineralization nearby.
Field identification & locations
Identify by its distinctive 'pistachio green' color and extreme hardness (will scratch glass). Common in areas with ancient volcanic activity like the Appalachian Mountains, Lake Superior region, and California coast.
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