metamorphic
Greenstone
Metabasalts and metavolcanics
Hardness: 5-6 on the Mohs scale; Color: Dark green, grayish-green, or olive-green; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline or fine-grained; Cleavage: None distinct; Specific gravity: 2.7-3.0.
- Hardness
- 5-6 on the Mohs scale
- Color
- Dark green, grayish-green, or olive-green
- 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-green; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline or fine-grained; Cleavage: None distinct; 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 or subduction zones over millions of years.
Uses & applications
Used locally as decorative gravel, in landscaping, road construction, and historically by indigenous peoples for making polished stone tools and adzes.
Geological facts
Greenstone is well-known in New Zealand (known as pounamu or greenstone/nephrite jade, though true greenstone refers to metamorphosed basalt), and it indicates areas of ancient tectonic activity and ocean floor subduction.
Field identification & locations
Can be identified in the field by its distinct greenish coloration due to minerals like chlorite, actinolite, and epidote. Commonly found in ancient greenstone belts and mountainous regions with altered volcanic rocks.
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