igneous
Tumbled river pebble, likely basaltic andesite
Fine-grained mafic volcanic rock; composition likely plagioclase, pyroxene, and minor iron oxides
AI-generated identification · may be incorrectHardness about 5.5–6.5 Mohs; olive-brown to gray, dull to faintly earthy luster, very fine-grained and massive with no visible cleavage. Its smooth rounded shape results from prolonged water abrasion.
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Physical properties
Hardness about 5.5–6.5 Mohs; olive-brown to gray, dull to faintly earthy luster, very fine-grained and massive with no visible cleavage. Its smooth rounded shape results from prolonged water abrasion.
Formation & geological history
Likely formed as lava that cooled rapidly at or near Earth’s surface, then weathered and was transported in a river or shoreline environment. Exact geological age and locality cannot be determined from the photograph.
Uses & applications
Used as decorative landscaping stone, polished pebble, craft material, and occasionally aggregate; generally has little gem value.
Geological facts
The small pale circular spots may be weathered phenocrysts, vesicles, or alteration patches, but photography alone cannot distinguish them reliably.
Field identification & locations
Identify by its heavy, opaque, fine-grained texture, lack of glassy appearance, and absence of obvious quartz or large crystals; a streak, hardness, density, and thin-section test would refine identification. Common in volcanic terrains and stream gravels worldwide.
