metamorphic
Greenschist (Chlorite Schist)
Greenschist (Metamorphic rock dominated by chlorite, actinolite, and epidote)
Hardness: 3.5 to 4.5 on Mohs scale; Color: Dark green to greyish-green; Luster: Pearly to vitreous; Crystal Structure: Foliated (schistose texture with visible alignment of platy minerals); Cleavage: Perfect basal cleavage in individual mineral grains.
- Hardness
- 3
- Color
- Dark green to greyish-green
- Luster
- Pearly to vitreous
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Physical properties
Hardness: 3.5 to 4.5 on Mohs scale; Color: Dark green to greyish-green; Luster: Pearly to vitreous; Crystal Structure: Foliated (schistose texture with visible alignment of platy minerals); Cleavage: Perfect basal cleavage in individual mineral grains.
Formation & geological history
Formed through the regional metamorphism of mafic igneous rocks (like basalt) under relatively low temperature (300 to 450 °C) and pressure conditions, typically in subduction zones or mountain-building environments across various geological eras.
Uses & applications
Primarily used as crushed stone for construction and road fill. Occasionally used as ornamental stone, for carvings, or as a source of industrial minerals if high in specific silicates. Historically used for making stone tools due to its toughness.
Geological facts
Greenschist represents the 'greenschist facies,' a major metamorphic grade used by geologists to determine the historical pressure and temperature history of a region's crust. It is often associated with gold deposits in 'greenstone belts.'
Field identification & locations
Identify in the field by its distinct green hue, flaky or 'platy' texture that sparkles in the light, and its tendency to split into thin sheets. Common in the Appalachian Mountains, Scottish Highlands, and the Alps. Collectors should look for variations containing visible garnets.
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