metamorphic
Greenstone
Metabasalt / Metavolcanic rock
Hardness: 5-6 on the Mohs scale; Color: Dark green, grayish-green, or speckled green due to chlorite, epidote, and actinolite; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline to fine-grained; Specific gravity: 2.7-3.0
- Hardness
- 5-6 on the Mohs scale
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 on the Mohs scale; Color: Dark green, grayish-green, or speckled green due to chlorite, epidote, and actinolite; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline to fine-grained; Specific gravity: 2.7-3.0
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks, typically basalt, gabbro, or diabase, under high pressure and low temperatures in ancient orogenic belts.
Uses & applications
Used historically for axes and adzes by indigenous peoples, and occasionally as decorative stone, tumbled stones, or in landscaping.
Geological facts
Greenstone gets its characteristic color from secondary green minerals like chlorite, epidote, and actinolite that replace the original pyroxenes and plagioclase during metamorphism.
Field identification & locations
Identify by its dense, fine-grained texture and pervasive green coloration. Commonly found in ancient greenstone belts of the Canadian Shield, Australia, and various mountainous regions worldwide.
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