igneous
Beach Pebble (Basalt / Greywacke)
Basalt (or fine-grained Sedimentary Greywacke)
Hardness 6-7 on Mohs scale; dull to matte earth-toned grey color; smooth rounded cubic-like shape due to wave action erosion; fine-grained microcrystalline texture.
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Physical properties
Hardness 6-7 on Mohs scale; dull to matte earth-toned grey color; smooth rounded cubic-like shape due to wave action erosion; fine-grained microcrystalline texture.
Formation & geological history
Formed as volcanic lava (basalt) or dense micro-grained marine sediment (greywacke). Over thousands of years, wave and sand attrition smoothed and rounded the specimen on coastal beaches.
Uses & applications
Commonly collected as pocket stones or worry stones; used in landscaping, decorative stone arrangements, or aquarium gravel.
Geological facts
Continuous wave action tumbling stones on beaches naturally creates rounded geometric shapes over decades, acting like a giant natural rock tumbler.
Field identification & locations
Identified by its water-worn, smooth surface, heavy density, dull greyish color, and lack of visible large mineral grains.
