metamorphic
Greenstone / Greenschist
Greenschist (composed of Chlorite, Epidote, and Actinolite)
Hardness: 3.5 to 5 on Mohs scale. Color: various shades of green, from dark forest green to grayish-green. Luster: dull to silky. Crystal structure: foliated or massive. Specific gravity: 2.8-3.0. Often has a somewhat greasy or waxy feel.
- Hardness
- 3
- Luster
- dull to silky
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Physical properties
Hardness: 3.5 to 5 on Mohs scale. Color: various shades of green, from dark forest green to grayish-green. Luster: dull to silky. Crystal structure: foliated or massive. Specific gravity: 2.8-3.0. Often has a somewhat greasy or waxy feel.
Formation & geological history
Formed by low-grade regional metamorphism of mafic igneous rocks (like basalt) at low temperatures (200-400°C) and moderate pressures. This process is common in orogenic belts where tectonic plates collide.
Uses & applications
Historically used for making stone tools and ornaments. Today it is used as decorative stone, in construction as crushed stone, and occasionally for carving or in jewelry if the quality is high.
Geological facts
The term 'greenstone' is a general field term for any basaltic rock that has been turned green by metamorphism. Many Neolithic axe heads found in Europe were crafted from this material due to its toughness.
Field identification & locations
Identified by its distinctive green hue and often a schistose (layered) or slightly shiny texture caused by chlorite and mica minerals. Commonly found in mountain ranges, coastal areas of California, and ancient shield regions like Canada or Western Australia.
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