igneous
Dark basaltic rock, possibly scoriaceous basalt
Basalt; predominantly plagioclase and pyroxene, with possible olivine and iron oxides
AI-generated identification · may be incorrectFine- to medium-grained, dark gray to brown, dull to slightly glassy, and apparently massive with small vesicles or weathered cavities. Typical basalt hardness is about Mohs 6, with no obvious cleavage and specific gravity around 2.8–3.1.
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Physical properties
Fine- to medium-grained, dark gray to brown, dull to slightly glassy, and apparently massive with small vesicles or weathered cavities. Typical basalt hardness is about Mohs 6, with no obvious cleavage and specific gravity around 2.8–3.1.
Formation & geological history
An extrusive igneous rock formed when mafic lava cooled rapidly at or near Earth’s surface, commonly in volcanic flows. Basalt forms from ancient to modern volcanism; its exact age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road material, riprap, railroad ballast, and building stone; attractive polished pieces may be collected, though this specimen appears ordinary.
Geological facts
Its dark color reflects abundant ferromagnesian minerals and iron-bearing oxides. The reddish-brown areas may represent oxidation or weathering rather than a distinct mineral.
Field identification & locations
Identify it by its dark color, fine texture, heavy weight, and resistance to scratching; a glassy streak or abundant bubbles would support scoriaceous basalt. Common worldwide in volcanic regions, including Hawaii, Iceland, India, and oceanic crust.
