metamorphic
Greenschist
Chlorite schist
Hardness: 2-3.5 (Mohs scale), Color: Greenish-grey to dark green, Luster: Pearly to sub-metallic (due to mica), Crystal Structure: Monoclinic (foliated), Cleavage: Perfect basal cleavage, Specific Gravity: 2.7–2.9
- Hardness
- 2-3
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Physical properties
Hardness: 2-3.5 (Mohs scale), Color: Greenish-grey to dark green, Luster: Pearly to sub-metallic (due to mica), Crystal Structure: Monoclinic (foliated), Cleavage: Perfect basal cleavage, Specific Gravity: 2.7–2.9
Formation & geological history
Formed through low-grade metamorphism (greenschist facies) of mafic igneous rocks or sediment, typically at temperatures of 300 to 450 °C and moderate pressure. Common in continental orogenic belts.
Uses & applications
Primarily used as decorative stone, crushed stone for construction, and occasionally for carving ornaments or building facades. It is also an important indicator rock for geologists mapping metamorphic zones.
Geological facts
The 'green' in greenschist comes from the presence of minerals like chlorite, epidote, and actinolite. It marks a specific range of metamorphic conditions known as the 'Greenschist Facies'.
Field identification & locations
Identified by its distinctive green hue, foliated or 'schistose' platy texture, and its soft, somewhat soapy feel if high in chlorite. Found in mountain ranges such as the Alps, Appalachians, and the Scottish Highlands. Collectors should look for the characteristic glimmer of mica minerals.
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