igneous
Tumbled river pebble, likely weathered basalt
Basalt; fine-grained mafic volcanic rock, commonly containing plagioclase, pyroxene, and iron oxides
AI-generated identification · may be incorrectDark brown-gray, rounded and smoothly weathered, with a dull-to-subvitreous luster and faint speckling; hardness about 5–6 Mohs, no visible cleavage, and typical specific gravity around 2.8–3.0. The image alone cannot confirm the exact rock type.
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Physical properties
Dark brown-gray, rounded and smoothly weathered, with a dull-to-subvitreous luster and faint speckling; hardness about 5–6 Mohs, no visible cleavage, and typical specific gravity around 2.8–3.0. The image alone cannot confirm the exact rock type.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, then was rounded by river, beach, or glacial abrasion. Basalt ranges from Precambrian to modern age and occurs in oceanic crust and volcanic provinces.
Uses & applications
Used as aggregate, road stone, riprap, and decorative landscaping material; attractive polished pieces may be used in simple crafts, but this specimen has little gem value.
Geological facts
Its smooth shape records prolonged abrasion and transport. Brown coloration commonly reflects surface weathering and oxidation of iron-bearing minerals.
Field identification & locations
Look for fine grain, high density, dark color, and weak attraction to a magnet if iron-rich; a fresh broken surface should be gray-black. Common worldwide near volcanic rocks and streambeds.
