igneous
Tumbled dark stone, likely basalt or iron-rich pebble
Probable basalt; composition chiefly plagioclase and pyroxene, possibly with iron oxides
AI-generated identification · may be incorrectDark brown to gray, dull-to-subvitreous luster, fine-grained and rounded by tumbling or erosion; basalt hardness is about 6 Mohs, with no visible cleavage and typical specific gravity of 2.8–3.0.
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Physical properties
Dark brown to gray, dull-to-subvitreous luster, fine-grained and rounded by tumbling or erosion; basalt hardness is about 6 Mohs, with no visible cleavage and typical specific gravity of 2.8–3.0.
Formation & geological history
Likely formed as an extrusive volcanic rock when mafic lava cooled rapidly, generally from geologically young to ancient volcanic environments; the smooth shape reflects natural abrasion or polishing. The image alone cannot establish exact age or composition.
Uses & applications
Common basalt is used for aggregate, roadstone, landscaping, and occasionally lapidary objects; ordinary pebbles have little jewelry or collector value.
Geological facts
Small pits or pale spots may represent vesicles, weathering, or embedded feldspar; a magnet response would suggest appreciable magnetite but is not diagnostic.
Field identification & locations
Look for a uniformly fine texture, high density, dark color, and absence of obvious sand grains or layering; a streak, hardness, magnetism, and specific-gravity test would improve identification. Basalt is widespread in volcanic regions and river gravels.
