metamorphic
Greenstone
Greenschist (containing chlorite, epidote, and actinolite)
Hardness: 5-7 (Mohs scale); Color: Dull green to dark forest green; Luster: Dull to waxy; Structure: Finely crystalline to foliated; Specific Gravity: 2.8-3.0; often features subtle banding or a water-worn, smooth texture.
- Hardness
- 5-7 (Mohs scale)
- Color
- Dull green to dark forest green
- Luster
- Dull to waxy
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Physical properties
Hardness: 5-7 (Mohs scale); Color: Dull green to dark forest green; Luster: Dull to waxy; Structure: Finely crystalline to foliated; Specific Gravity: 2.8-3.0; often features subtle banding or a water-worn, smooth texture.
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks (like basalt or gabbro). This process occurs at relatively low temperatures (300 to 450 °C) and moderate pressures, where green minerals like chlorite replace the original minerals.
Uses & applications
Historically used for making stone tools (celts and axes) due to its toughness. Today it is used as decorative stone, crushed stone for construction, and occasionally in lapidary work for cabochons or garden ornaments.
Geological facts
Greenstone belts represent some of the oldest known rocks on Earth, dating back to the Archean Eon. Many are associated with major gold deposits, such as those in Western Australia and Canada.
Field identification & locations
Identify in the field by its distinct 'sea-foam' to 'olive' green color and its resistance to weathering compared to surrounding rocks. Often found in ancient volcanic island arc terrains and mountain ranges. Collectors should look for river-tumbled specimens which show 'rind' or banding.
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