metamorphic
Greenstone
Metabasalt / Greenschist
Hardness: 5-6 on the Mohs scale; Color: Green, grayish-green, or dark green; Luster: Dull to sub-greasy; Crystal structure: Microcrystalline to fine-grained metamorphic texture; Cleavage: Poor or indistinct.
- Hardness
- 5-6 on the Mohs scale
- Color
- Green, grayish-green, or dark green
- Luster
- Dull to sub-greasy
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Physical properties
Hardness: 5-6 on the Mohs scale; Color: Green, grayish-green, or dark green; Luster: Dull to sub-greasy; Crystal structure: Microcrystalline to fine-grained metamorphic texture; Cleavage: Poor or indistinct.
Formation & geological history
Formed through the low-grade regional metamorphism of mafic igneous rocks, such as basalt or gabbro, typically under greenschist facies conditions involving heat and pressure in ancient volcanic or oceanic environments.
Uses & applications
Historically used by indigenous peoples for making stone axes and adzes due to its toughness; occasionally used as a decorative stone or in landscaping.
Geological facts
The characteristic green color is imparted by secondary green minerals such as chlorite, epidote, and actinolite, which replace the original minerals during metamorphism.
Field identification & locations
Found worldwide in ancient greenstone belts, often associated with Precambrian shields. Field identification relies on its distinct greenish coloration and fine-grained, tough texture resulting from low-grade metamorphism of volcanic rocks.
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