igneous
Weathered volcanic rock, likely basaltic andesite
Basaltic andesite to andesite; fine-grained plagioclase–pyroxene volcanic rock
AI-generated identification · may be incorrectTypically dark gray to brown with weathered reddish surfaces, dull to faintly lusterous, and fine-grained; hardness about 5.5–6.5 Mohs, no obvious cleavage, and specific gravity roughly 2.6–2.8. The specimen appears massive and heavily weathered, with possible vesicles or surface cavities.
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Physical properties
Typically dark gray to brown with weathered reddish surfaces, dull to faintly lusterous, and fine-grained; hardness about 5.5–6.5 Mohs, no obvious cleavage, and specific gravity roughly 2.6–2.8. The specimen appears massive and heavily weathered, with possible vesicles or surface cavities.
Formation & geological history
Formed when intermediate-to-mafic lava cooled at or near Earth’s surface, probably during a volcanic episode; its exact geological age cannot be determined from the photograph. Weathering and abrasion produced the rounded shape and rusty coloration.
Uses & applications
Used as crushed aggregate, road stone, riprap, and occasionally building or paving stone; generally little jewelry value.
Geological facts
The pink, brown, and gray colors commonly result from oxidation of iron-bearing minerals and alteration of the rock. Exact identification would require a fresh surface, mineral inspection, and ideally thin-section or chemical analysis.
Field identification & locations
Look for a dense, fine-grained texture, dark gray fresh interior, weak magnetism, and tiny plagioclase crystals; distinguish it from basalt by its generally lighter/intermediate composition. Common in volcanic belts and exposed lava flows.
