metamorphic
Greenstone / Greenschist
Greenschist (composed primarily of Chlorite, Epidote, and Actinolite)
Hardness: 3.5-5 (Mohs); Color: Pale to dark green, grayish-green; Luster: Dull to pearly; Crystal structure: Foliated or schistose texture; Cleavage: Good in one direction due to mica-like minerals; Specific gravity: 2.85-3.00.
- Hardness
- 3
- Color
- Pale to dark green, grayish-green
- Luster
- Dull to pearly
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Physical properties
Hardness: 3.5-5 (Mohs); Color: Pale to dark green, grayish-green; Luster: Dull to pearly; Crystal structure: Foliated or schistose texture; Cleavage: Good in one direction due to mica-like minerals; Specific gravity: 2.85-3.00.
Formation & geological history
Formed through low-grade metamorphism (greenschist facies) of mafic igneous rocks (like basalt) at temperatures of 300-450 degrees Celsius and moderate pressure. Often associated with ancient mountain building and convergent plate boundaries.
Uses & applications
Commonly used as crushed stone for road construction and aggregate; historically used for axes, chisels, and decorative carvings; occasionally used for tiles or garden landscaping.
Geological facts
The green color comes from minerals like chlorite and epidote that form during metamorphism. It is a major component of the 'Greenstone Belts' which contain some of the oldest rocks and significant gold deposits on Earth.
Field identification & locations
Identify by its characteristic green hue and slightly foliated (layered) or splintery texture. Frequently found in regions with ancient volcanic activity like the Appalachian Mountains, Scotland, or the Canadian Shield. Collectors look for pieces with visible actinolite crystals.
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