metamorphic
Greenstone (or Greywacke/Metasediment Pebble)
Metamorphosed Mafic Rock / Chlorite Schist
Hardness: 5-6 Mohs. Color: Dusky blue-green to teal-grey with a light brownish-tan quartz/calcite vein. Luster: Dull to smooth silky satin when water-worn. Structure: Fine-grained, non-porous metamorphic fabric. Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Luster
- Dull to smooth silky satin when water-worn
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Physical properties
Hardness: 5-6 Mohs. Color: Dusky blue-green to teal-grey with a light brownish-tan quartz/calcite vein. Luster: Dull to smooth silky satin when water-worn. Structure: Fine-grained, non-porous metamorphic fabric. Specific Gravity: 2.8-3.0.
Formation & geological history
Formed through low-grade regional metamorphism (greenschist facies) of oceanic basalt, volcanic ash, or muddy sandstone. The thin vein represents secondary hydrothermal fluids depositing quartz or carbonate along a fracture during tectonic movement.
Uses & applications
Commonly collected as river or beach pebbles, used in decorative landscaping, lapidary polishing, and historically for stone tools due to toughness.
Geological facts
Greenish coloration in metamorphic rocks like greenstone is typically caused by the growth of minerals such as chlorite, epidote, or actinolite under moderate heat and pressure.
Field identification & locations
Identify by its smooth rounded river/beach cobble shape, distinctive greyish-teal or bluish-green hue, and cross-cutting mineral vein. Widely found along glacial drift, riverbeds, and ocean beaches worldwide.
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