igneous
Rounded river pebble, probably basaltic-andesite or fine-grained igneous rock
Likely microcrystalline basalt/andesite; exact identification requires testing
AI-generated identification · may be incorrectGray-green, fine-grained, massive, dull to faintly earthy luster, with no visible crystals or cleavage; likely Mohs hardness about 5.5–6.5 and specific gravity roughly 2.7–3.0.
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Physical properties
Gray-green, fine-grained, massive, dull to faintly earthy luster, with no visible crystals or cleavage; likely Mohs hardness about 5.5–6.5 and specific gravity roughly 2.7–3.0.
Formation & geological history
A volcanic rock formed when mafic to intermediate lava cooled relatively quickly, then was naturally rounded by stream or coastal abrasion. Its precise geological age and source cannot be determined from the photograph.
Uses & applications
Usually collected as a natural curiosity, teaching specimen, or decorative pebble; crushed equivalents are used as aggregate and road material, but this individual has little commercial value.
Geological facts
The smooth, near-spherical shape is transport-worn rather than a crystal form. A streak, magnetism, acid reaction, and fresh broken surface would help distinguish basalt from andesite, altered volcanic rock, or dark sandstone.
Field identification & locations
Common in riverbeds, beaches, glacial deposits, and volcanic terrains worldwide. Look for fine interlocking grains, absence of obvious layering, and possible weak attraction to a magnet; a hand lens may reveal tiny feldspar or pyroxene crystals.
