metamorphic
Greenschist
Greenschist (Chlorite-actinolite schist)
Hardness: 3.5-4.5; Color: Dull green, grayish-green, or dark emerald; Luster: Pearly to vitreous on foliation planes; Crystal structure: Monoclinic; Cleavage: High fissility (easy to split into thin sheets); Specific gravity: 2.8-3.3.
- Hardness
- 3
- Color
- Dull green, grayish-green, or dark emerald
- Luster
- Pearly to vitreous on foliation planes
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Physical properties
Hardness: 3.5-4.5; Color: Dull green, grayish-green, or dark emerald; Luster: Pearly to vitreous on foliation planes; Crystal structure: Monoclinic; Cleavage: High fissility (easy to split into thin sheets); Specific gravity: 2.8-3.3.
Formation & geological history
Formed through low-grade metamorphism (greenschist facies) of mafic igneous rocks like basalt or gabbro. This occurs at temperatures of 300 to 450 degrees Celsius and depths of 5 to 15 km.
Uses & applications
Used primarily as decorative stone, for garden landscaping, and historically for building material. Some varieties with high chlorite content are used as a source of industrial minerals.
Geological facts
The 'green' color is specifically caused by minerals like chlorite, epidote, and actinolite. It is a key indicator for geologists that a region has undergone low-intensity regional metamorphism.
Field identification & locations
Identify in the field by its characteristic greenish hue and 'schistose' texture (distinct layering). It is commonly found in mountain belts like the Appalachian Mountains and the Swiss Alps. Collectors should look for shiny mica-like surfaces along the cracks.
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