metamorphic
Greenstone (Greenschist)
Greenschist facies rock (containing chlorite, epidote, actinolite)
Hardness: 3.5 to 4.5. Color: Dull green to grayish-green. Luster: Dull to silky. Crystal structure: Microcrystalline to foliated. Specific gravity: 2.8-3.0.
- Hardness
- 3
- Color
- Dull green to grayish-green
- Luster
- Dull to silky
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Physical properties
Hardness: 3.5 to 4.5. Color: Dull green to grayish-green. Luster: Dull to silky. Crystal structure: Microcrystalline to foliated. Specific gravity: 2.8-3.0.
Formation & geological history
Formed through regional metamorphism of mafic igneous rocks (like basalt) under low temperature and moderate pressure. Often associated with ancient oceanic crust or mountain-building events.
Uses & applications
Used historically for stone tools like celts and adzes. Currently used for gravel, road base, and decorative landscaping. Sometimes used in jewelry when polished as 'New Zealand Jade' or nephrite-like material.
Geological facts
The 'green' in greenstone comes from minerals like chlorite and epidote that form during low-grade metamorphism. It is a major component of ancient 'Greenstone Belts' which are some of the oldest rock formations on Earth.
Field identification & locations
Identify by its characteristic dull green color and relative hardness (cannot be easily scratched with a penny but can be with steel). Commonly found in riverbeds or coastal areas near tectonic plate boundaries.
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