igneous
Tumbled river pebble, likely basaltic rock
Fine-grained mafic volcanic rock; composition commonly plagioclase, pyroxene, and iron–magnesium minerals
AI-generated identification · may be incorrectDark gray-brown, rounded and water-worn, with dull to weakly waxy luster and indistinct fine texture. Estimated Mohs hardness 5–6; massive, non-cleaving, and typically dense (specific gravity about 2.8–3.1).
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Physical properties
Dark gray-brown, rounded and water-worn, with dull to weakly waxy luster and indistinct fine texture. Estimated Mohs hardness 5–6; massive, non-cleaving, and typically dense (specific gravity about 2.8–3.1).
Formation & geological history
Likely weathered from a basalt or related volcanic flow, then rounded by stream or wave abrasion. Basalt commonly formed during the Cenozoic or older volcanic episodes, though this individual pebble’s age cannot be determined visually.
Uses & applications
Used as landscaping stone, garden decoration, aggregate, and occasionally in polished-stone collections; it has little jewelry value unless unusually attractive or patterned.
Geological facts
The smooth shape indicates prolonged transport or deliberate tumbling. Subtle blue-gray, brown, and rusty tones may reflect alteration of iron-bearing minerals.
Field identification & locations
Common in riverbeds, beaches, glacial deposits, and basalt-bearing regions. A hand lens may reveal tiny dark crystals; a streak test is usually gray, and it should not fizz with dilute hydrochloric acid.
