metamorphic
Greenstone (Epidosite or Altered Basalt)
Epidosite (Ca2(Al, Fe)3(SiO4)3(OH))
Hardness: 6-7 (Mohs scale), Color: Dull to pistachio green, Luster: Dull to waxy, Crystal Structure: Monoclinic (microcrystalline in this form), Specific Gravity: 3.2-3.5
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dull to pistachio green, Luster: Dull to waxy, Crystal Structure: Monoclinic (microcrystalline in this form), Specific Gravity: 3.2-3.5
Formation & geological history
Formed through low-grade regional or hydrothermal metamorphism of mafic igneous rocks (like basalt or gabbro) under relatively low pressure and temperature, specifically the greenschist facies.
Uses & applications
Used primarily as decorative stone, crushed stone for construction, and occasionally for lapidary work like cabochons or tumbled stones for hobbyists.
Geological facts
Greenstone belts are historically significant as they are often associated with major world gold and silver deposits formed in Archean and Proterozoic eras.
Field identification & locations
Identify in the field by its distinct dull green color and hardness (should not be easily scratched by steel). Commonly found in ancient shields such as the Canadian Shield or along tectonic suture zones.
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