metamorphic
Greenstone (Epidosite)
Epidosite (Metamorphosed Basalt/Diabase)
Hardness: 6-7 (Mohs scale), Color: Pistachio green to dark gray-green, Luster: Dull to waxy, Crystal Structure: Microcrystalline, Cleavage: None (subconchoidal fracture), Specific Gravity: 3.2-3.5
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Pistachio green to dark gray-green, Luster: Dull to waxy, Crystal Structure: Microcrystalline, Cleavage: None (subconchoidal fracture), Specific Gravity: 3.2-3.5
Formation & geological history
Formed through the low-grade metamorphism of mafic igneous rocks (like basalt or diabase) in hydrothermal environments or subduction zones, typically during the Paleozoic or Mesozoic eras.
Uses & applications
Used primarily as decorative river stones, landscaping materials, and occasionally in stone carving or as a lapidary material for cabochons.
Geological facts
Greenstone is a general field term for any dark, greenish, altered igneous rock. The green color is primarily due to the presence of minerals like epidote, chlorite, and actinolite.
Field identification & locations
Identify by its characteristic 'pistachio' green patches and high density. Commonly found in riverbeds near ancient mountain ranges (like the Appalachians or Cascades). Collectors look for smooth, water-worn cobbles with high epidote content.
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