igneous
Iron-rich basalt or hematitic volcanic rock
Likely basalt (plagioclase–pyroxene rock) with iron-oxide staining; exact identification requires testing
AI-generated identification · may be incorrectDark reddish-brown, dull to slightly earthy luster, massive and fine-grained with irregular fracture; typically Mohs 5–6 and specific gravity about 2.8–3.3. The color may reflect hematite or weathering rather than the primary rock.
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Physical properties
Dark reddish-brown, dull to slightly earthy luster, massive and fine-grained with irregular fracture; typically Mohs 5–6 and specific gravity about 2.8–3.3. The color may reflect hematite or weathering rather than the primary rock.
Formation & geological history
Probably formed as rapidly cooled mafic lava, generally in the Cenozoic or older; oxidation during weathering produced the reddish coloration. The image alone cannot establish age or locality.
Uses & applications
Common basalt is used for aggregate, roadstone, riprap, and occasionally building stone; these small rough pieces have little commercial or jewelry value.
Geological facts
Basalt commonly contains microscopic plagioclase and pyroxene, sometimes olivine or magnetite. A strong magnet response would suggest abundant magnetite; a red streak or powder indicates iron oxides.
Field identification & locations
Look for a fine-grained texture, high density, dark color, and absence of visible quartz; test with a steel file, streak plate, magnet, and dilute acid. Common worldwide, especially volcanic regions, but the specimen could also be hematite-rich slag or another iron-bearing rock.
