metamorphic
Greenstone
Metabasalt (often contains Chlorite, Actinolite, and Epidote)
Hardness: 5-7 Mohs; Color: Dull green to dark green with brownish weathering; Luster: Dull to waxy; Crystal structure: Fine-grained to aphanitic; Cleavage: None to poor; Specific gravity: 2.85-3.1
- Hardness
- 5-7 Mohs
- Color
- Dull green to dark green with brownish weathering
- Luster
- Dull to waxy
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Physical properties
Hardness: 5-7 Mohs; Color: Dull green to dark green with brownish weathering; Luster: Dull to waxy; Crystal structure: Fine-grained to aphanitic; Cleavage: None to poor; Specific gravity: 2.85-3.1
Formation & geological history
Formed through the low-grade regional metamorphism of mafic igneous rocks (like basalt). Common in Precambrian shields and volcanic belts where ancient oceanic crust underwent heat and pressure.
Uses & applications
Historically used for making stone tools and axes; currently used as construction aggregate, crushed stone for road base, and occasionally as decorative landscaping stone.
Geological facts
The specific green color is caused by the presence of chlorite and epidote. Greenstones are often part of 'Greenstone Belts' which are major sources of gold and silver deposits worldwide.
Field identification & locations
Identified by its signature dull green color and toughness. It is harder than a steel nail and won't fizz with acid. Common in the Canadian Shield, Western Australia, and the Appalachian Mountains.
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