metamorphic
Greenstone / Greenschist
Greenschist facies metamorphic rock (composed primarily of chlorite, actinolite, and epidote)
Hardness: 5-6 on the Mohs scale depending on specific mineral makeup; Color: Various shades of green, grayish-green, or olive; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline or fine-grained foliated; Cleavage: Poor to moderate; Specific gravity: 2.7-3.0
- Hardness
- 5-6 on the Mohs scale depending on specific mineral makeup
- Color
- Various shades of green, grayish-green, or olive
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 on the Mohs scale depending on specific mineral makeup; Color: Various shades of green, grayish-green, or olive; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline or fine-grained foliated; Cleavage: Poor to moderate; Specific gravity: 2.7-3.0
Formation & geological history
Formed through regional metamorphism of mafic igneous rocks (such as basalt, gabbro, or diabase) under relatively low temperature and moderate pressure conditions, typically in ancient subduction zones or mountain-building events.
Uses & applications
Used locally as decorative stone, crushed stone for construction, and occasionally for lapidary purposes or making polished worry stones and cabochons.
Geological facts
The characteristic green color comes from the abundance of green minerals like chlorite, epidote, and actinolite formed during the hydrothermal alteration and low-grade metamorphism of iron and magnesium-rich minerals.
Field identification & locations
Can be identified in the field by its distinct greenish hue and water-worn pebble or cobble form in glacial till, riverbeds, or beaches. Often found in regions with ancient tectonic collision zones and greenstone belts.
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