metamorphic
Greenstone / Greenschist
Metamorphosed mafic igneous rock (Greenschist facies)
Hardness: 5-6 (Mohs scale), Color: dull green to grayish-green, Luster: dull to vitreous, Texture: fine-grained, sometimes foliated or massive, Cleavage: poor
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Physical properties
Hardness: 5-6 (Mohs scale), Color: dull green to grayish-green, Luster: dull to vitreous, Texture: fine-grained, sometimes foliated or massive, Cleavage: poor
Formation & geological history
Formed through the regional metamorphism of mafic igneous rocks like basalt or gabbro under low temperature and moderate pressure conditions, typically during mountain-building events.
Uses & applications
Used historically for stone tools (axes), modernly as decorative garden stone, construction aggregate, and occasionally for lapidary work if highly silicified.
Geological facts
The green color comes from minerals like chlorite, epidote, and actinolite. It was highly prized by indigenous cultures for making 'celt' axes because of its toughness.
Field identification & locations
Identify by the characteristic olive or dull green color and smooth, water-worn texture when found in riverbeds. Common in ancient mountain belts like the Appalachians or the Cascades.
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