igneous
Weathered volcanic rock, likely basaltic andesite
Basaltic andesite (fine-grained plagioclase–pyroxene rock; provisional visual identification)
AI-generated identification · may be incorrectDark gray-brown, weathered, fine-grained and massive, with dull earthy luster and small lighter mineral grains; likely hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.6–2.9.
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Physical properties
Dark gray-brown, weathered, fine-grained and massive, with dull earthy luster and small lighter mineral grains; likely hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.6–2.9.
Formation & geological history
Likely formed when lava cooled relatively quickly at or near Earth’s surface, probably in a volcanic arc or continental volcanic setting. Its exact age cannot be determined from the photograph; brown coloration reflects surface weathering and oxidation.
Uses & applications
Used as crushed aggregate, road material, riprap, and occasionally building stone; generally little jewelry value.
Geological facts
Basaltic andesite lies compositionally between basalt and andesite and commonly contains plagioclase, pyroxene, and sometimes olivine or iron oxides.
Field identification & locations
In the field, test for a dense, nonporous, fine-grained texture and dark fresh interior; a streak, hand lens, and acid test help distinguish it from weathered sedimentary rock. Common in volcanic regions worldwide.
