metamorphic
Greenstone
Greenschist (metamorphosed mafic igneous rock)
Hardness: 3.5-5 (variable); Color: Dull green, grayish-green, or emerald green; Luster: Dull to waxy; Texture: Fine-grained, often foliated; Specific Gravity: 2.8-3.0; Contains chlorite, epidote, and actinolite.
- Hardness
- 3
- Color
- Dull green, grayish-green, or emerald green
- Luster
- Dull to waxy
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Physical properties
Hardness: 3.5-5 (variable); Color: Dull green, grayish-green, or emerald green; Luster: Dull to waxy; Texture: Fine-grained, often foliated; Specific Gravity: 2.8-3.0; Contains chlorite, epidote, and actinolite.
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks like basalt or gabbro, occurring at depths of 2-15 km and temperatures of 300-450°C. Many date back to the Precambrian or Paleozoic eras.
Uses & applications
Historically used for making stone tools and axes. Today, it is used for architectural stone, garden landscaping, gravel, and occasionally for minor decorative carvings.
Geological facts
The 'Greenstone Belts' are some of the oldest parts of the Earth's crust, often associated with gold and copper deposits. The green color is primarily due to the presence of chlorite and epidote minerals.
Field identification & locations
Identify in the field by its distinct greenish hue and lack of prominent crystalline structure. It is commonly found in ancient mountain belts following riverbeds or shorelines in regions like the Pacific Northwest, Canada, or Scandinavia.
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