metamorphic
Greenstone / Greenschist
Chlorite schist / Epidiorite / Metabasalt
Hardness: 3.5 to 5.5 (variable); Color: Dull green, olive to forest green; Luster: Dull to slightly silky; Crystal structure: Fine-grained, often foliated or massive; Specific gravity: 2.8 to 3.0.
- Hardness
- 3
- Color
- Dull green, olive to forest green
- Luster
- Dull to slightly silky
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Physical properties
Hardness: 3.5 to 5.5 (variable); Color: Dull green, olive to forest green; Luster: Dull to slightly silky; Crystal structure: Fine-grained, often foliated or massive; Specific gravity: 2.8 to 3.0.
Formation & geological history
Formed by low-grade regional metamorphism of mafic igneous rocks (like basalt or gabbro) under relatively low temperature and pressure, typically in subduction zones or mountain-building regions.
Uses & applications
Used historically for stone tools and weapons (axes); currently used as crushed stone for construction, road base, and occasionally for decorative landscaping or carving.
Geological facts
The green color is primarily due to the presence of minerals like chlorite, epidote, and actinolite. The term 'Greenstone belt' is used to describe ancient geological formations that often contain significant gold and nickel deposits.
Field identification & locations
Identify by its characteristic dull green hue and lack of visible large crystals. It reflects the transformation of volcanic seafloor crust. Found commonly in the Appalachian Mountains, Lake Superior region, and Western Australia.
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