metamorphic
Greenstone
Metabasalt / Metamorphosed Igneous Rock
Hardness: 6-7 on Mohs scale; Color: Grayish-green to dark green; Luster: Dull to waxy; Crystal structure: Fine-grained to aphanitic; Cleavage: Generally poor; Specific Gravity: 2.8 to 3.0
- Hardness
- 6-7 on Mohs scale
- Color
- Grayish-green to dark green
- Luster
- Dull to waxy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Grayish-green to dark green; Luster: Dull to waxy; Crystal structure: Fine-grained to aphanitic; Cleavage: Generally poor; Specific Gravity: 2.8 to 3.0
Formation & geological history
Formed through low-grade metamorphism of basaltic rocks under high pressure and low temperatures, typically in subduction zones or greenstone belts ranging from the Archean era (4 to 2.5 billion years ago) to more recent tectonic events.
Uses & applications
Used historically for tools and weapons, and currently as crushed stone for road construction, decorative gravel in landscaping, and occasionally as a semi-precious stone for carvings or jewelry.
Geological facts
Greenstone belts contain some of the oldest known rocks on Earth and are often associated with significant gold and copper deposits. The green color is due to minerals like chlorite, epidote, and actinolite.
Field identification & locations
Identify in the field by its distinct dull green hue and toughness. It is frequently found in riverbeds or coastal areas near ancient tectonic plate boundaries. Collectors look for smooth, well-worn river cobbles with visible mineral veins.
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