igneous
Rounded fine-grained river pebble, likely andesite
Probable andesite (plagioclase feldspar with pyroxene and/or amphibole; exact identification requires testing)
AI-generated identification · may be incorrectGray-brown, dull, and fine-grained with small visible mineral specks; rounded by abrasion. Typical andesite has Mohs hardness about 6, an interlocking crystalline texture, and no prominent cleavage in the whole rock.
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Physical properties
Gray-brown, dull, and fine-grained with small visible mineral specks; rounded by abrasion. Typical andesite has Mohs hardness about 6, an interlocking crystalline texture, and no prominent cleavage in the whole rock.
Formation & geological history
Likely formed when intermediate-composition lava cooled at or near Earth’s surface, then became rounded during transport in water. Andesites occur in volcanic arcs and span many geological ages.
Uses & applications
This pebble has little commercial value; andesite is used locally as aggregate, paving stone, and building stone.
Geological facts
The image shows a hand-sized, water-worn specimen; its precise rock type cannot be confirmed from appearance alone.
Field identification & locations
Look for a dense gray groundmass with tiny feldspar crystals and test hardness or streak; similar pebbles occur in streams and beaches near volcanic or mixed-rock terrain.
