igneous
Polished dark gray stone, likely basalt or fine-grained andesite
Basalt/andesite; primarily plagioclase feldspar, pyroxene, and possibly olivine or magnetite
AI-generated identification · may be incorrectFine-grained, rounded and polished, dark gray with a subtly sparkly granular surface; typically hardness 5–6 Mohs, dull to faintly vitreous luster, no visible cleavage, and specific gravity about 2.7–3.1.
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Physical properties
Fine-grained, rounded and polished, dark gray with a subtly sparkly granular surface; typically hardness 5–6 Mohs, dull to faintly vitreous luster, no visible cleavage, and specific gravity about 2.7–3.1.
Formation & geological history
An extrusive volcanic rock formed when basaltic to intermediate lava cooled rapidly at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes. The smooth shape is human-made by tumbling or polishing.
Uses & applications
Used as landscaping stone, aggregate, pavers, countertops, and decorative tumbled stone; generally low collector value unless unusually patterned or sourced from a notable locality.
Geological facts
The specimen’s uniform dark color and fine texture are consistent with basalt, though a photograph cannot distinguish it confidently from andesite, diabase, or dark metamorphic rock.
Field identification & locations
Look for a dense, fine-grained texture, dark color, lack of layering, and possible tiny pale feldspar crystals; a streak, magnetism test, and hand lens would improve identification. Common worldwide, especially near volcanic regions.
