igneous
Fine-grained dark volcanic rock, likely basalt or scoria
Basaltic rock; predominantly plagioclase feldspar, pyroxene, and minor olivine/iron oxides
AI-generated identification · may be incorrectDark gray-brown, fine-grained and granular with a dull to weakly sparkly luster; likely Mohs hardness 5–6, no visible cleavage, and moderate-to-high specific gravity (~2.8–3.1). The rounded shape appears naturally worn or tumbled, and the surface may contain tiny vesicles.
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Physical properties
Dark gray-brown, fine-grained and granular with a dull to weakly sparkly luster; likely Mohs hardness 5–6, no visible cleavage, and moderate-to-high specific gravity (~2.8–3.1). The rounded shape appears naturally worn or tumbled, and the surface may contain tiny vesicles.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic or older volcanic activity; exact age and locality cannot be determined from the photograph.
Uses & applications
Common basalt is used as crushed aggregate, road stone, riprap, and occasionally as dimension stone; attractive pieces may be collected, but this specimen has little commercial value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms lava flows, dikes, and volcanic islands. If noticeably porous and lightweight, it may instead be scoria.
Field identification & locations
Identify it by its dark color, fine texture, lack of obvious layering, and high density; a streak test, magnet response, and fresh fracture would help distinguish basalt from scoria or dark sedimentary rock. Common worldwide, especially in volcanic regions.
