metamorphic
Greenstone
Metabasalt / Greenstone
Hardness: 6-7 on Mohs scale. Color: Dull green, grayish-green, or dark green. Luster: Dull to sub-vitreous. Crystal Structure: Fine-grained, often massive. Cleavage: Poor or absent. Specific Gravity: 2.8 - 3.2.
- Hardness
- 6-7 on Mohs scale
- Color
- Dull green, grayish-green, or dark green
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dull green, grayish-green, or dark green. Luster: Dull to sub-vitreous. Crystal Structure: Fine-grained, often massive. Cleavage: Poor or absent. Specific Gravity: 2.8 - 3.2.
Formation & geological history
Formed through low-grade metamorphism (greenschist facies) of mafic igneous rocks like basalt. This process occurs under low temperature and high pressure, often in subduction zones or mountain-building regions.
Uses & applications
Used primarily as crushed stone for road construction and aggregate. Historically used for making stone tools (axes) and occasionally used in ornamental building facades.
Geological facts
The green color comes from minerals like chlorite, epidote, and actinolite which replace the original minerals in the basalt. Large belts of greenstone are called 'Greenstone Belts' and are often billions of years old.
Field identification & locations
Identify by the distinctive greenish hue and toughness. It is typically harder and more resistant than surrounding shale or slate. Common in ancient cratonic shields like those in Canada, Australia, and the Appalachians.
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