metamorphic
Greenstone (River Pebble)
Metabasalt / Greenschist
Hardness: 5-7 Mohs; Color: Dull-green to grey-green with yellowish epidote or feldspar inclusions; Luster: Dull to waxy when wet; Structure: Dense, fine-grained; Cleavage: None/Poor.
- Hardness
- 5-7 Mohs
- Luster
- Dull to waxy when wet
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Physical properties
Hardness: 5-7 Mohs; Color: Dull-green to grey-green with yellowish epidote or feldspar inclusions; Luster: Dull to waxy when wet; Structure: Dense, fine-grained; Cleavage: None/Poor.
Formation & geological history
Formed through the low-grade metamorphism of mafic igneous rocks (like basalt) under high pressure and low temperature conditions, often in subduction zones or mountain-building environments. This specimen has been rounded by fluvial (river) erosion.
Uses & applications
Commonly used as decorative garden stones, in landscaping, as aquarium gravel, and occasionally as a source for primitive stone tools or craft lapidary work.
Geological facts
The term 'greenstone' is a general field term for any compact, dark-green altered igneous rock. The green color is primarily due to the presence of minerals like chlorite, actinolite, and epidote.
Field identification & locations
Identify by its characteristic 'sea-green' hue and hardness (won't be scratched by a steel nail). Look for these in riverbeds or coastal areas near ancient volcanic belts. It is a common indicator of regional metamorphism.
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