igneous
Rounded gray pebble, likely basalt or andesite
Fine-grained volcanic rock, probably basaltic-andesite; exact identification requires testing
AI-generated identification · may be incorrectGray, dull to slightly earthy luster, rounded by abrasion, and apparently fine-grained with scattered pale grains or weathering spots. Typical hardness is about 5–6 Mohs; cleavage is absent and specific gravity commonly 2.7–3.0.
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Physical properties
Gray, dull to slightly earthy luster, rounded by abrasion, and apparently fine-grained with scattered pale grains or weathering spots. Typical hardness is about 5–6 Mohs; cleavage is absent and specific gravity commonly 2.7–3.0.
Formation & geological history
Likely solidified lava that cooled rapidly at or near Earth’s surface, then became rounded in a stream, beach, or glacial environment. Its precise geological age and formation setting cannot be determined from the photograph.
Uses & applications
Commonly used as aggregate, road stone, riprap, and landscaping material; small attractive pebbles may be collected or used decoratively.
Geological facts
Basalt is the most widespread volcanic rock and forms much of oceanic crust. Andesitic rocks are compositionally intermediate between basalt and rhyolite.
Field identification & locations
Look for a dense, nonlayered texture, lack of visible large crystals, and possible attraction to a magnet if iron-rich; a streak, acid, hardness, and fresh broken surface would improve identification. Common worldwide, especially volcanic regions and gravel deposits.
