igneous
Rounded gray stone, possibly basalt or river-worn volcanic rock
Likely basalt; mineral composition dominated by plagioclase feldspar and pyroxene, with possible olivine
AI-generated identification · may be incorrectDark gray, smooth and strongly rounded, dull to subtly silky luster, fine-grained texture with small pits or vesicles; hardness about 5–6 Mohs, no obvious cleavage, specific gravity roughly 2.8–3.1.
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Physical properties
Dark gray, smooth and strongly rounded, dull to subtly silky luster, fine-grained texture with small pits or vesicles; hardness about 5–6 Mohs, no obvious cleavage, specific gravity roughly 2.8–3.1.
Formation & geological history
Probably formed as a volcanic igneous rock from cooled mafic lava, then rounded and smoothed by stream, beach, or glacial transport; its exact geological age cannot be determined from the image.
Uses & applications
Common basalt is used as aggregate, road stone, building material, ballast, and landscaping rock; attractive polished pieces may be sold as décor or inexpensive specimens.
Geological facts
The surface pits may represent vesicles—gas bubbles preserved during lava cooling—or weathering cavities. The exceptionally smooth shape indicates prolonged abrasion in moving water or surf.
Field identification & locations
Look for a dense, dark fine-grained interior, minimal visible crystals, and a streak that is generally gray rather than metallic; a fresh broken surface and magnet test can help distinguish basalt from slag or other stones. Common worldwide, especially volcanic regions and riverbeds.
