igneous
Likely dark basalt or mafic rock
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine or magnetite
AI-generated identification · may be incorrectFine-grained, dark gray to black, with a dull to weakly vitreous luster; hardness about 6 on Mohs scale, no obvious cleavage, and typical specific gravity of 2.8–3.0. The blurred image prevents reliable determination of vesicles, crystals, or surface texture.
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Physical properties
Fine-grained, dark gray to black, with a dull to weakly vitreous luster; hardness about 6 on Mohs scale, no obvious cleavage, and typical specific gravity of 2.8–3.0. The blurred image prevents reliable determination of vesicles, crystals, or surface texture.
Formation & geological history
Basalt forms when low-silica magma cools rapidly at or near Earth’s surface, commonly in lava flows, oceanic crust, and volcanic islands. Individual specimens may range from recent eruptions to ancient rocks billions of years old.
Uses & applications
Used as crushed aggregate, road base, railway ballast, dimension stone, and landscaping material; attractive polished pieces may be collected but are generally low-value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Magnetic response may occur if it contains abundant magnetite.
Field identification & locations
Field identification relies on its black, dense, fine-grained appearance and lack of visible quartz; a streak test, magnet test, and fresh broken surface help distinguish it from slag or weathered rocks. Common worldwide, especially volcanic regions and oceanic terrains.
