igneous
Weathered mafic rock (probable basalt or gabbro fragment)
Basalt–gabbroic rock; chiefly plagioclase feldspar and pyroxene, possibly olivine
AI-generated identification · may be incorrectDark brown-gray, rough and granular with dull to faintly earthy luster; likely Mohs hardness 5–6, massive structure, no obvious cleavage, and specific gravity about 2.8–3.1. The brown surface likely reflects weathering or iron staining.
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Physical properties
Dark brown-gray, rough and granular with dull to faintly earthy luster; likely Mohs hardness 5–6, massive structure, no obvious cleavage, and specific gravity about 2.8–3.1. The brown surface likely reflects weathering or iron staining.
Formation & geological history
Likely formed when mafic magma cooled, either rapidly as basalt at the surface or slowly as gabbro underground; its exact geological age cannot be determined from the image. Weathering produced the rounded, oxidized exterior.
Uses & applications
Common basalt is used as crushed aggregate, road stone, riprap, and occasionally dimension stone; ordinary fragments have little jewelry or collector value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. Gabbro has essentially the same chemistry but larger visible crystals due to slower cooling.
Field identification & locations
Look for a dense, dark rock that is harder than glass, often weakly magnetic, and may show tiny feldspar crystals; a fresh broken surface would distinguish basalt from gabbro. Common worldwide, especially in volcanic regions and river gravels.
