metamorphic
Greenstone
Metabasalt / Greenschist
Hardness: 5-6 on the Mohs scale; Color: Dark green, grayish-green, or olive; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline to cryptocrystalline (composed of chlorite, epidote, and actinolite); Cleavage: Indistinct; Specific Gravity: 2.7-3.0.
- Hardness
- 5-6 on the Mohs scale
- Color
- Dark green, grayish-green, or olive
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 on the Mohs scale; Color: Dark green, grayish-green, or olive; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline to cryptocrystalline (composed of chlorite, epidote, and actinolite); Cleavage: Indistinct; Specific Gravity: 2.7-3.0.
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks, such as basalt or gabbro, typically in underwater environments like ocean floors or convergent plate boundaries over millions of years.
Uses & applications
Used locally as decorative stones, in lapidary work for cabochons, and historically for stone tools like adzes and axes due to its toughness.
Geological facts
The green color is primarily due to the presence of secondary minerals like chlorite and epidote that replace the original pyroxenes and calcic plagioclase during alteration.
Field identification & locations
Can be identified in the field by its distinct greenish hue and high toughness. Common in ancient shield areas and mountain belts worldwide, particularly in greenstone belts.
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