metamorphic
Greenstone Pebbles (Basalt/Diabase)
Metamorphosed Mafic Rock (Greenstone)
Hardness: 6-7 (Mohs scale), Color: Dull olive green to dark grayish-green, Luster: Dull to waxy when wet, Crystal structure: Fine-grained (aphanitic), Specific gravity: 2.8-3.0
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dull olive green to dark grayish-green, Luster: Dull to waxy when wet, Crystal structure: Fine-grained (aphanitic), Specific gravity: 2.8-3.0
Formation & geological history
Formed through the low-grade metamorphism of mafic igneous rocks like basalt or gabbro under high pressure and low temperature (greenschist facies), often in oceanic crust environments.
Uses & applications
Commonly used as high-quality construction aggregate, landscaping stones, and sometimes for small lapidary crafts or aquarium decor.
Geological facts
The green color is primarily due to the presence of chlorite, actinolite, and epidote minerals. This specific smooth shape indicates it has been tumbled by water in a lake or river for long periods.
Field identification & locations
Identify by the distinct green cast compared to common gray stones; it will not scratch easily with a steel blade. Frequently found on beaches around the Great Lakes (Isle Royale Greenstone is a famous variant).
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