igneous
Dark volcanic rock, likely basalt
Basalt; predominantly plagioclase feldspar and pyroxene, commonly with minor olivine and magnetite
AI-generated identification · may be incorrectAppears dark gray-brown, massive, fine-grained, and dull to weakly vitreous, with irregular weathering and no obvious cleavage. Typical hardness is about 6 Mohs and specific gravity about 2.8–3.0; the surface may be weathered or coated, reducing diagnostic reliability.
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Physical properties
Appears dark gray-brown, massive, fine-grained, and dull to weakly vitreous, with irregular weathering and no obvious cleavage. Typical hardness is about 6 Mohs and specific gravity about 2.8–3.0; the surface may be weathered or coated, reducing diagnostic reliability.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and flood-basalt provinces. Its exact age cannot be determined from the photograph; basalt ranges from ancient Archean rocks to modern eruptions.
Uses & applications
Crushed basalt is widely used for road aggregate, concrete, rail ballast, and rock wool; attractive dense pieces may be collected or used decoratively, but this specimen is not visibly gem-grade.
Geological facts
The rounded shape may result from water transport or weathering rather than original volcanic form. A fresh broken surface would reveal its characteristic fine crystalline texture.
Field identification & locations
Common worldwide, including oceanic islands, mid-ocean ridges, India’s Deccan Traps, Iceland, and the western United States. Confirm with a fresh surface, streak (usually gray), magnetism from iron oxides, and absence of fizz with dilute acid.
