igneous
Tumbled dark stone, possibly basalt or smoky quartz
Uncertain from image; likely fine-grained basalt (plagioclase–pyroxene) or a dark quartz-rich pebble
AI-generated identification · may be incorrectSmooth, rounded, and likely machine-tumbled; dark gray-brown with subdued vitreous to dull luster. Basalt has Mohs hardness ~5–6 and no visible cleavage, while smoky quartz is harder (~7) and glassier.
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Physical properties
Smooth, rounded, and likely machine-tumbled; dark gray-brown with subdued vitreous to dull luster. Basalt has Mohs hardness ~5–6 and no visible cleavage, while smoky quartz is harder (~7) and glassier.
Formation & geological history
If basalt, it formed from rapidly cooled mafic lava, commonly Cenozoic to Precambrian in age; if quartz, it crystallized in silica-rich veins or igneous rocks and was later rounded by erosion and tumbling.
Uses & applications
Used as a lapidary curiosity, worry stone, or decorative pebble; basalt is also widely used for aggregate and dimension stone.
Geological facts
The photograph is insufficient for confident identification because grain size and diagnostic crystals are obscured by polishing and blur.
Field identification & locations
Test hardness against glass, inspect the edge under magnification, and check streak: basalt is usually gray-brown and opaque, whereas quartz may scratch glass and transmit light at thin edges. Common sources include volcanic terrains and river gravels.
