metamorphic
Greenschist
Greenschist facies rock (containing chlorite, actinolite, albite, and epidote)
Hardness: 3.5-5 (Mohs scale); Color: green to dark greyish-green with oxidized orange-brown weathering; Luster: vitreous to silky/dull; Crystal structure: foliated (schistose) with fine-grained texture; Cleavage: prominent slaty to schistose foliation
- Hardness
- 3
- Luster
- vitreous to silky/dull
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Physical properties
Hardness: 3.5-5 (Mohs scale); Color: green to dark greyish-green with oxidized orange-brown weathering; Luster: vitreous to silky/dull; Crystal structure: foliated (schistose) with fine-grained texture; Cleavage: prominent slaty to schistose foliation
Formation & geological history
Formed through the regional metamorphism of mafic igneous rocks (like basalt) or sedimentary rocks under low-temperature (300-450°C) and moderate-pressure conditions. It typically represents the Phanerozoic or Precambrian eras depending on location.
Uses & applications
Used primarily in construction as crushed stone or landscaping rock. Occasionally used as decorative material for paving or as minor building stone. Limited value in jewelry but sometimes used for lapidary carvings.
Geological facts
The name 'Greenschist' comes from the presence of green minerals like chlorite. It indicates a specific metamorphic 'facies' that helps geologists determine the heat and pressure history of an entire mountain range.
Field identification & locations
Identify in the field by its distinct foliated (layered) appearance and green tint. It often splits into thin plates or flakes. Commonly found in folded mountain belts and ancient shield regions. Collectors should look for silky sheen in the foliation planes.
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