igneous
Weathered igneous rock, likely basaltic lava (uncertain)
Fine-grained mafic volcanic rock, probably basalt; exact identification requires testing
AI-generated identification · may be incorrectDark gray to brown, strongly weathered, rough and granular with possible vesicles or altered mineral patches; basalt typically has Mohs hardness about 6, dull to subvitreous luster, no cleavage, and specific gravity around 2.8–3.1.
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Physical properties
Dark gray to brown, strongly weathered, rough and granular with possible vesicles or altered mineral patches; basalt typically has Mohs hardness about 6, dull to subvitreous luster, no cleavage, and specific gravity around 2.8–3.1.
Formation & geological history
Likely cooled rapidly from mafic lava at or near Earth’s surface, then altered by oxidation, water, and physical weathering; age cannot be determined from the photograph. Some pieces may instead be iron-rich sediment or industrial slag, so chemical testing is needed.
Uses & applications
Basalt is widely used as crushed aggregate, roadstone, riprap, ballast, and occasionally building stone; attractive dense pieces may be collected but these specimens have limited gem value.
Geological facts
Basalt commonly contains plagioclase, pyroxene, and sometimes olivine or magnetite. Weathering can produce brown iron-oxide coatings and obscure the original texture.
Field identification & locations
Look for a dense dark matrix, tiny interlocking crystals, magnetic response from magnetite, and lack of obvious layering; a streak, acid, magnet, and fresh broken surface would improve identification. Common worldwide, especially volcanic regions and oceanic crust.
