igneous
Likely basalt
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, commonly with olivine
AI-generated identification · may be incorrectDark gray to black, fine-grained, generally dull to slightly glassy; hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.8–3.0. The image is low-resolution, but the mottled texture may indicate weathering or small crystalline grains.
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Physical properties
Dark gray to black, fine-grained, generally dull to slightly glassy; hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.8–3.0. The image is low-resolution, but the mottled texture may indicate weathering or small crystalline grains.
Formation & geological history
Forms when mafic lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, lava flows, and volcanic islands; specimens may range from Precambrian to modern.
Uses & applications
Used extensively as crushed aggregate, road base, railroad ballast, and dimension stone; attractive polished pieces are occasionally used decoratively, but this specimen has little gem value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Vesicles, if present, can indicate gas-rich lava; none are clearly visible here.
Field identification & locations
Identify by its very dark color, heavy feel, fine texture, and lack of visible large crystals; common worldwide, especially at mid-ocean ridges, Hawaii, Iceland, and continental volcanic fields. A hand lens and streak, hardness, and magnetic tests would improve identification.
