igneous
Fine-grained dark gray rock core, likely basalt or andesite
Probable basaltic-andesitic volcanic rock; exact identification requires thin section or geochemical testing
AI-generated identification · may be incorrectDark gray-brown, dense, fine-grained, dull to weakly subvitreous luster with small pale mineral grains or weathering spots. Likely hardness about 5–6 Mohs, massive texture, no obvious cleavage, and specific gravity roughly 2.7–3.0.
Identified More igneous →
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Physical properties
Dark gray-brown, dense, fine-grained, dull to weakly subvitreous luster with small pale mineral grains or weathering spots. Likely hardness about 5–6 Mohs, massive texture, no obvious cleavage, and specific gravity roughly 2.7–3.0.
Formation & geological history
Likely an igneous drill-core specimen formed when mafic to intermediate lava cooled, probably in a volcanic or subvolcanic setting. Its geological age cannot be determined from the photograph and depends on the drilling locality.
Uses & applications
Basalt and andesite are used as crushed aggregate, roadstone, riprap, concrete additive, and dimension stone; this core is mainly useful for geological exploration and testing.
Geological facts
The cylindrical pieces in the background are drill core, indicating subsurface exploration. The specimen’s fine grain suggests relatively rapid cooling, but the visible texture is insufficient to distinguish basalt confidently from andesite or altered volcanic rock.
Field identification & locations
Identify with a hand lens, streak, magnetic response, thin section, and geochemical analysis; basalt is commonly magnetic and contains plagioclase plus pyroxene, while andesite is generally lighter and more silica-rich. Common settings include volcanic arcs, lava flows, and oceanic crust.
