igneous
Water-worn brown stone, likely basalt or chert
Indeterminate; possible fine-grained basalt (plagioclase–pyroxene) or ferruginous chert (microcrystalline SiO₂)
AI-generated identification · may be incorrectSmooth, rounded cobble with brown to dark gray coloration, dull-to-waxy luster, and no visible crystals or cleavage; likely Mohs hardness 5.5–7, depending on composition. The surface appears naturally weathered and polished by abrasion.
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Physical properties
Smooth, rounded cobble with brown to dark gray coloration, dull-to-waxy luster, and no visible crystals or cleavage; likely Mohs hardness 5.5–7, depending on composition. The surface appears naturally weathered and polished by abrasion.
Formation & geological history
Probably formed as a dense fine-grained volcanic rock or chemical sediment, then transported and rounded by water; its precise geological age and origin cannot be determined from the photograph.
Uses & applications
Commonly collected as a beach, river, or lapidary stone and may be polished for decorative use; unexceptional pieces have little commercial value.
Geological facts
The brown color may result from iron-oxide weathering. A streak, hardness, magnetic, acid, and specific-gravity tests are needed for reliable identification.
Field identification & locations
Look for a glassy conchoidal fracture and inability to scratch with a steel knife for chert; basalt is usually softer, may be weakly magnetic, and often leaves a gray streak. Common in riverbeds, beaches, and volcanic terrains.
