igneous
Dark mafic rock, likely basalt
Basalt; predominantly plagioclase feldspar and pyroxene, with possible olivine and iron-titanium oxides
AI-generated identification · may be incorrectFine-grained, dark gray to black, dull to slightly glassy; hardness about 6, generally massive with no obvious cleavage, and specific gravity roughly 2.8–3.0. The specimen’s rough, compact appearance is consistent with basalt, though the image cannot confirm its mineralogy.
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Physical properties
Fine-grained, dark gray to black, dull to slightly glassy; hardness about 6, generally massive with no obvious cleavage, and specific gravity roughly 2.8–3.0. The specimen’s rough, compact appearance is consistent with basalt, though the image cannot confirm its mineralogy.
Formation & geological history
Basalt forms when low-silica mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and hotspot environments. It ranges from ancient Archean rocks to actively forming modern lava.
Uses & applications
Used extensively as crushed aggregate, road base, railroad ballast, building stone, and occasionally fiber insulation; attractive polished pieces are used decoratively. This small unverified fragment has minimal commercial value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Vesicles, olivine crystals, or a fine-grained groundmass can help distinguish varieties.
Field identification & locations
Look for a dense black/gray rock with tiny crystals, possible vesicles, and weak attraction to a magnet from iron minerals; a hand lens and streak, density, or thin-section test improves identification. Common worldwide, especially Hawaii, Iceland, India’s Deccan Traps, and oceanic islands.
