metamorphic
Greenstone
Metamorphic mafic rock (chlorite-actinolite-epidote schist)
Hardness: 5-6 on the Mohs scale; Color: Dark green, grayish-green, or mottled greenish-black; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline to fine-grained massive or schistose; Specific gravity: 2.7-3.0
- Hardness
- 5-6 on the Mohs scale
- Color
- Dark green, grayish-green, or mottled greenish-black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 on the Mohs scale; Color: Dark green, grayish-green, or mottled greenish-black; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline to fine-grained massive or schistose; Specific gravity: 2.7-3.0
Formation & geological history
Formed through low-grade regional metamorphism (greenschist facies) of mafic igneous rocks such as basalt, diabase, or gabbro, typically occurring in ancient oceanic crust or volcanic arcs.
Uses & applications
Historically used by indigenous peoples for fashioning stone axes and adzes due to its toughness; used locally as crushed stone or decorative aggregate.
Geological facts
Greenstone is exceptionally tough because its interlocking microscopic mineral crystals resist fracturing, which made it a prized material for prehistoric Neolithic stone tools worldwide.
Field identification & locations
Identified in the field by its distinct greenish coloration and compact, hard texture. Commonly found in ancient greenstone belts, shield regions, and areas of past tectonic subduction zones.
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