metamorphic
Greenstone
Metamorphic mafic rock (greenschist facies)
Hardness: 5-6 on Mohs scale; Color: Dark green, grayish-green, or greenish-black; Luster: Dull to sub-vitreous; Crystal structure: Fine-grained, crypto-crystalline, or felted mineral texture; Cleavage: Generally poor or massive due to microcrystalline interlocking minerals; Specific Gravity: 2.7 to 3.0
- Hardness
- 5-6 on Mohs scale
- Color
- Dark green, grayish-green, or greenish-black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 on Mohs scale; Color: Dark green, grayish-green, or greenish-black; Luster: Dull to sub-vitreous; Crystal structure: Fine-grained, crypto-crystalline, or felted mineral texture; Cleavage: Generally poor or massive due to microcrystalline interlocking minerals; Specific Gravity: 2.7 to 3.0
Formation & geological history
Formed by the low-grade regional metamorphism (greenschist facies) of mafic igneous rocks such as basalt, diabase, or gabbro, typically in underwater environments or ancient greenstone belts dating from the Archean to Proterozoic eons.
Uses & applications
Historically used by indigenous peoples for making polished stone axes and adzes due to its toughness; occasionally cut and polished as an ornamental stone, cabochons, or collected by rockhounds.
Geological facts
Greenstones are famous for preserving some of the earliest evidence of Earth's crust and ancient tectonic activity, often found in ancient shields and cratons globally.
Field identification & locations
Can be identified in the field by its distinct greenish hue, dense feel, and lack of visible coarse crystals. Found globally in ancient orogenic belts, stream beds, and glacial deposits.
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