igneous
Iron-rich volcanic rock, likely basalt or scoriaceous basalt
Basalt; predominantly plagioclase feldspar, pyroxene, and iron oxides, possibly with hematite/goethite staining
AI-generated identification · may be incorrectDark gray to reddish-brown, fine-grained and massive with rough, locally vesicular texture; typically Mohs 5–6, dull to slightly vitreous luster, no obvious cleavage, and specific gravity about 2.8–3.2.
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Physical properties
Dark gray to reddish-brown, fine-grained and massive with rough, locally vesicular texture; typically Mohs 5–6, dull to slightly vitreous luster, no obvious cleavage, and specific gravity about 2.8–3.2.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface; the red coloration reflects oxidation of iron-bearing minerals, commonly during weathering. Its exact geological age cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, roadstone, riprap, and occasionally building stone; attractive pieces are collected as field specimens. It is not normally a jewelry material.
Geological facts
The specimen may alternatively be an iron-stained volcanic breccia or weathered andesite; a photograph cannot reliably distinguish these. A dark streak and magnetic response would support abundant iron oxides or magnetite.
Field identification & locations
Common in volcanic regions worldwide, including Hawaii, Iceland, the Pacific Northwest, India, and oceanic crust. Identify it by its dark fine-grained matrix, heavy feel, weak-to-moderate magnetism, and lack of visible large crystals; a fresh broken surface is diagnostic.
