igneous
Weathered igneous pebble, likely basaltic andesite
Fine-grained mafic to intermediate volcanic rock; chiefly plagioclase feldspar, pyroxene, and possibly olivine or magnetite
AI-generated identification · may be incorrectDark gray-brown, mottled, and subrounded with a dull to faintly waxy luster; likely hardness 5–6, compact texture, no visible cleavage, and approximately 2.7–3.0 specific gravity. Pale patches and dark spots may reflect altered minerals or vesicles.
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Physical properties
Dark gray-brown, mottled, and subrounded with a dull to faintly waxy luster; likely hardness 5–6, compact texture, no visible cleavage, and approximately 2.7–3.0 specific gravity. Pale patches and dark spots may reflect altered minerals or vesicles.
Formation & geological history
Likely formed when lava cooled rapidly at or near Earth’s surface, then became rounded and weathered in a stream or beach environment. Exact geological age and identification require a fresh surface, streak, density, and ideally thin-section or chemical testing.
Uses & applications
Used locally as aggregate, riprap, road stone, and landscaping material; this ordinary pebble has little jewelry or commercial value.
Geological facts
Its brown coloration probably represents surface oxidation or weathering rather than the original rock color. The image does not show diagnostic crystals clearly enough for a precise species-level identification.
Field identification & locations
Common in volcanic terrains and derived river gravels worldwide; look for a fine-grained dark interior, magnetic response, and absence of layering or strong foliation. A fresh broken surface and acid/magnet tests can help distinguish it from altered sedimentary rocks.
