igneous
Iron-stained weathered volcanic rock (probable basalt/andesite)
Altered basaltic–andesitic rock, chiefly plagioclase and pyroxene with iron oxides/hydroxides
AI-generated identification · may be incorrectHardness about 5–6; dull, fine-grained, gray-brown to reddish-brown with dark weathered patches and rusty limonite staining. Massive texture, no obvious cleavage, and relatively high density (approximately 2.7–3.1).
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Physical properties
Hardness about 5–6; dull, fine-grained, gray-brown to reddish-brown with dark weathered patches and rusty limonite staining. Massive texture, no obvious cleavage, and relatively high density (approximately 2.7–3.1).
Formation & geological history
Likely an extrusive igneous rock formed when lava cooled at or near Earth’s surface, then chemically weathered and oxidized in a soil or surface environment. Its precise age and identity cannot be determined from the photograph alone.
Uses & applications
Common basalt and andesite are used as crushed aggregate, road stone, riprap, and building stone; this weathered piece has little commercial or jewelry value.
Geological facts
The orange-brown coloration commonly results from oxidation of iron-bearing minerals into hematite and limonite. Dark areas may represent fresher mafic minerals, manganese staining, or secondary alteration.
Field identification & locations
In the field, test for a fine-grained interlocking texture, strong heft, lack of layering, and hardness sufficient to scratch glass; a streak, magnetism, and acid test can help distinguish basalt from iron-rich ore or altered rock. Common in volcanic terrains worldwide.
