igneous
Weathered vesicular volcanic rock, likely basaltic scoria
Vesicular basalt/scoria; chiefly plagioclase, pyroxene, and iron oxides
AI-generated identification · may be incorrectDark brown to gray, fine-grained and dull, with abundant small vesicles and weathering coatings; hardness about 5–6 Mohs, generally massive, with no obvious cleavage. The rounded form indicates substantial water or stream abrasion.
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Physical properties
Dark brown to gray, fine-grained and dull, with abundant small vesicles and weathering coatings; hardness about 5–6 Mohs, generally massive, with no obvious cleavage. The rounded form indicates substantial water or stream abrasion.
Formation & geological history
Formed when gas-rich basaltic lava cooled rapidly, trapping bubbles; later oxidation and weathering produced the brown surface. Exact geological age cannot be determined from the photograph; such rocks range from recent volcanic deposits to ancient basalt flows.
Uses & applications
Commonly used as lightweight aggregate, landscaping stone, drainage material, and occasionally abrasive or decorative stone; this weathered cobble has little jewelry value.
Geological facts
Scoria is typically more vesicular and lighter than dense basalt, while basaltic composition gives it dark minerals and high density. Surface staining can obscure its original red-black volcanic color.
Field identification & locations
Look for vesicles, a fine crystalline texture, iron-rich dark minerals, and a relatively heavy feel; a streak, fresh broken surface, magnetism, and density test would improve identification. Common near volcanic fields and basaltic river gravels.
