igneous
Rounded gray river pebble, likely basalt or andesite
Fine-grained mafic volcanic rock; commonly basalt (plagioclase, pyroxene, and possible olivine)
AI-generated identification · may be incorrectDark gray, fine-grained, dull to weakly subvitreous luster, with no visible crystals or cleavage; Mohs hardness about 5–6 and specific gravity roughly 2.8–3.1. Its smooth elongated shape reflects abrasion during transport, not its original crystal form.
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Physical properties
Dark gray, fine-grained, dull to weakly subvitreous luster, with no visible crystals or cleavage; Mohs hardness about 5–6 and specific gravity roughly 2.8–3.1. Its smooth elongated shape reflects abrasion during transport, not its original crystal form.
Formation & geological history
Likely formed as volcanic lava that cooled rapidly at or near Earth’s surface, then was rounded by river, beach, or glacial transport. The specimen’s geological age cannot be determined from the photograph.
Uses & applications
Primarily a common decorative or landscaping stone, paperweight, or craft material; not generally valuable for jewelry or construction in this small form.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly forms oceanic crust. Similar-looking pebbles may instead be andesite, fine-grained metamorphic rock, or weathered industrial aggregate.
Field identification & locations
Look for a uniformly fine texture, substantial weight, dark gray color, and absence of obvious layering; a streak, magnetism test, and fresh broken surface would improve identification. Common in volcanic terrains, river gravels, beaches, and glacial deposits.
