metamorphic
Greenstone
Metabasalt / Greenschist
Hardness of 5-6 on the Mohs scale, grayish-green to dark green color due to chlorite and epidote, dull to sub-greasy luster, fine-grained microcrystalline structure, massive and compact cleavage with specific gravity around 2.7-3.0.
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Physical properties
Hardness of 5-6 on the Mohs scale, grayish-green to dark green color due to chlorite and epidote, dull to sub-greasy luster, fine-grained microcrystalline structure, massive and compact cleavage with specific gravity around 2.7-3.0.
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks such as basalt, gabbro, or diabase, typically under moderate pressure and low temperatures in subduction zones or ocean basins.
Uses & applications
Historically used by indigenous cultures for making ground-stone axes and adzes; currently used in aggregate, road construction, and occasionally as an ornamental lapidary stone.
Geological facts
Greenstone is often associated with ancient greenstone belts, which contain some of the oldest exposed rock formations on Earth dating back over 3 billion years and frequently host significant gold deposits.
Field identification & locations
Easily identified by its distinctive grayish-green hue and fine-grained texture. Commonly found in ancient shield areas, mountain building belts, and regions with metamorphosed volcanic terrains. Look for it in glacial drift or stream gravels in glaciated regions.
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