metamorphic
Greenstone (Diabase or Metabasalt)
Metamorphosed Mafic Igneous Rock
Hardness: 6-7 (Mohs scale); Color: Dark green to grayish-green with light phenocrysts; Luster: Dull to sub-vitreous; Structure: Massive or foliated; SG: 2.8-3.0
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark green to grayish-green with light phenocrysts
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark green to grayish-green with light phenocrysts; Luster: Dull to sub-vitreous; Structure: Massive or foliated; SG: 2.8-3.0
Formation & geological history
Formed by low-grade metamorphism (greenschist facies) of mafic igneous rocks like basalt or diabase, often in orogenic belts. These typically date from the Archean to the Proterozoic eons.
Uses & applications
Used as crushed stone for road construction, riprap for erosion control, and occasionally as decorative stone or for lapidary work in jewelry.
Geological facts
Greenstone belts are historically significant for harboring major gold and silver deposits. The color comes from green minerals like chlorite, actinolite, and epidote.
Field identification & locations
Identify by its distinct greenish hue and hardness. It is commonly found in ancient shield areas like the Canadian Shield or the Appalachians. Collectors look for smooth river-tumbled specimens.
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