metamorphic
Greenstone
Greenschist / Meta-basalt
Hardness: 6-7 (Mohs scale); Color: Dull green, olive, to grayish-green; Luster: Stubby or dull; Crystal structure: Usually fine-grained or massive; Specific Gravity: 2.8 - 3.2.
- Hardness
- 6-7 (Mohs scale)
- Color
- Dull green, olive, to grayish-green
- Luster
- Stubby or dull
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dull green, olive, to grayish-green; Luster: Stubby or dull; Crystal structure: Usually fine-grained or massive; Specific Gravity: 2.8 - 3.2.
Formation & geological history
Formed through the low-grade metamorphism of mafic igneous rocks like basalt or gabbro under high pressure and low temperature conditions. Often associated with ancient volcanic arcs and plate tectonic subduction zones.
Uses & applications
Historically used for making stone tools (celts and axes) due to its toughness. Today used as crushed stone for construction, architectural veneers, and occasionally for carving or garden landscaping.
Geological facts
The green color comes from minerals like chlorite, epidote, and actinolite. Some of the oldest known rock formations on Earth are found in 'Greenstone Belts', which are critical for understanding early Earth history.
Field identification & locations
Identify by its distinctive greenish hue and toughness. It is commonly found in mountainous or glaciated regions with high metamorphic activity. Collectors look for smooth, river-worn cobbles like the one pictured.
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