metamorphic
Greenstone
Greenschist-facies basaltic rock
Hardness: 6-7 (Mohs scale); Color: Dull green, grayish-green, or forest green; Luster: Dull to waxy; Crystal structure: Microcrystalline; Cleavage: Poor or absent; Specific gravity: 2.85-3.0
- Hardness
- 6-7 (Mohs scale)
- Color
- Dull green, grayish-green, or forest green
- Luster
- Dull to waxy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dull green, grayish-green, or forest green; Luster: Dull to waxy; Crystal structure: Microcrystalline; Cleavage: Poor or absent; Specific gravity: 2.85-3.0
Formation & geological history
Formed through the regional metamorphism of mafic igneous rocks (like basalt or gabbro) under low temperature and moderate pressure. The green color comes from minerals like chlorite, epidote, and actinolite.
Uses & applications
Historically used for making stone tools (axes), construction aggregate, masonry, and sometimes used in jewelry or decorative carvings when high quality.
Geological facts
Greenstone belts are home to some of the oldest known rocks on Earth, dating back to the Archean Eon. They are often associated with major lode gold deposits.
Field identification & locations
Identify by its distinctive dull green hue and lack of visible crystalline structure in many river-worn specimens. Commonly found in ancient shield areas like the Superior Province in Canada or Western Australia.
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