metamorphic
Greenschist
Greenschist (comprising Actinolite, Chlorite, and Epidote)
Hardness: 3.5 to 5 on Mohs scale; Color: Pale green to olive green with white quartz/calcite veins; Luster: Pearly to dull; Crystal structure: Monoclinic; Cleavage: Good in one direction (slaty/schistose foliation); Specific gravity: 2.8 to 3.0
- Hardness
- 3
- Color
- Pale green to olive green with white quartz/calcite veins
- Luster
- Pearly to dull
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Physical properties
Hardness: 3.5 to 5 on Mohs scale; Color: Pale green to olive green with white quartz/calcite veins; Luster: Pearly to dull; Crystal structure: Monoclinic; Cleavage: Good in one direction (slaty/schistose foliation); Specific gravity: 2.8 to 3.0
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks (like basalt) at low temperatures (200-450°C) and moderate pressure. These typically date from several hundred million to billions of years old, often found in mountain belts.
Uses & applications
Used primarily as decorative stone, roofing material, and crushed stone for road construction. Occasionally used for small carvings or as architectural veneer.
Geological facts
Greenschist corresponds to the 'Greenschist Facies,' a specific range of metamorphic conditions. It gets its name from the green minerals (chlorite and actinolite) that form during the transformation of dark volcanic rocks.
Field identification & locations
Identify in the field by its distinct green hue and 'schistosity' (layered, platy appearance that can be split). Commonly found in the Appalachian Mountains, the Alps, and the Scottish Highlands. Look for it in areas with high past tectonic activity.
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