igneous
Rounded gray pebble, likely andesite
Probably andesite; identification from the photo is uncertain
AI-generated identification · may be incorrectGray, fine-grained, and dull, with scattered tiny mineral grains and no obvious layering. Typical andesite has Mohs hardness around 6, chiefly plagioclase with pyroxene or amphibole; crystal structure varies by mineral.
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Physical properties
Gray, fine-grained, and dull, with scattered tiny mineral grains and no obvious layering. Typical andesite has Mohs hardness around 6, chiefly plagioclase with pyroxene or amphibole; crystal structure varies by mineral.
Formation & geological history
Andesite forms when intermediate-composition lava cools, commonly in volcanic arcs at convergent plate boundaries. Its age cannot be determined from appearance alone.
Uses & applications
Ordinary pebbles are mainly decorative or collectible; andesite is also used locally as crushed stone and construction aggregate.
Geological facts
The specimen’s smooth, rounded shape suggests abrasion during transport by water or ice, rather than its original volcanic form.
Field identification & locations
A gray, fine-grained texture is consistent with andesite, but basalt and other rocks can look similar; a fresh broken surface or mineral testing would improve identification. Andesite occurs in volcanic regions worldwide, especially along the Pacific Ring of Fire.
