metamorphic
Greenstone
Metabasalt (composed mainly of chlorite, epidote, and actinolite)
Hardness: 6-7 (Mohs); Color: Pale green to dark grayish-green; Luster: Dull to earthy; Crystal structure: Microcrystalline with a massive texture; Specific gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs)
- Color
- Pale green to dark grayish-green
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Pale green to dark grayish-green; Luster: Dull to earthy; Crystal structure: Microcrystalline with a massive texture; Specific gravity: 2.8-3.0
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks (like basalt) under high pressure and low temperature, often in subduction zones or mountain-building environments.
Uses & applications
Used primarily as decorative crushed stone, construction aggregate, and occasionally for carving or in jewelry like pendants due to its pleasing green hue.
Geological facts
The 'green' in greenstone comes from minerals like chlorite and epidote that replace the original dark minerals in the basalt. Historically, it was used by Neolithic people to make high-quality stone axes.
Field identification & locations
Identify by its characteristic dull green color and fine-grained, tough texture that lacks obvious foliation. Common in ancient mountain belts and glacial till across North America and Europe.
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