metamorphic
Greenstone
Greenschist (commonly containing Chlorite, Actinolite, and Epidote)
Hardness: 6-7 on Mohs scale; Color: Dull to dark green; Luster: Dull or waxy; Crystal Structure: Generally fine-grained or massive; Cleavage: Poor or absent in beach-worn specimens; Specific Gravity: 2.8 - 3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dull to dark green
- Luster
- Dull or waxy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dull to dark green; Luster: Dull or waxy; Crystal Structure: Generally fine-grained or massive; Cleavage: Poor or absent in beach-worn specimens; Specific Gravity: 2.8 - 3.0.
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks (like basalt) at low temperatures and pressures. Often associated with ancient volcanic arcs and plate tectonic boundaries.
Uses & applications
Historically used for making stone tools (celts and axes) due to its toughness; currently used as decorative gravel, in landscaping, and occasionally as a minor gemstone or for carving.
Geological facts
Greenstone belts are some of the oldest known geological formations on Earth, frequently containing important deposits of gold and copper. The green color is primarily due to the presence of chlorite and epidote minerals.
Field identification & locations
Identify by its distinctive grayish-green or forest-green hue and smooth, rounded texture when found as a beach pebble. It is common on Pacific Northwest coasts and in areas with ancient volcanic activity. Collectors look for uniform color and lack of fractures.
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