igneous
Rounded river pebble, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; exact identification requires testing
AI-generated identification · may be incorrectDark olive-brown, smooth and water-worn with a dull to faintly waxy luster; likely hardness about 5–6 Mohs, massive (non-cleavable), and relatively dense. The surface coloration may reflect weathering or iron-oxide staining.
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Physical properties
Dark olive-brown, smooth and water-worn with a dull to faintly waxy luster; likely hardness about 5–6 Mohs, massive (non-cleavable), and relatively dense. The surface coloration may reflect weathering or iron-oxide staining.
Formation & geological history
Likely formed from rapidly cooled lava, then transported and rounded by stream or beach abrasion. Its exact geological age cannot be determined from the photograph.
Uses & applications
Suitable mainly as a decorative pebble, garden stone, craft material, or teaching specimen; not typically valuable for jewelry or construction in this small form.
Geological facts
Basalt commonly contains plagioclase and pyroxene, while andesite contains plagioclase with amphibole or pyroxene. A streak, fresh broken surface, magnet test, and hand lens would improve identification.
Field identification & locations
Common in volcanic regions and gravel deposits worldwide. Look for fine grain, high density, absence of visible layers, and possible weak magnetism; a uniformly brown appearance can also occur in weathered basalt.
