igneous
Dark basalt or basaltic volcanic rock
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and often olivine
AI-generated identification · may be incorrectBlack to dark gray, dull to subtly vitreous luster, fine-grained, massive, and irregularly rounded; Mohs hardness about 5–6, with no visible cleavage. The pits may be vesicles or weathering cavities; the glossy areas could reflect a naturally glassy surface or polishing.
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Physical properties
Black to dark gray, dull to subtly vitreous luster, fine-grained, massive, and irregularly rounded; Mohs hardness about 5–6, with no visible cleavage. The pits may be vesicles or weathering cavities; the glossy areas could reflect a naturally glassy surface or polishing.
Formation & geological history
Formed when basaltic lava rapidly cooled at or near Earth’s surface, commonly during Cenozoic to recent volcanism; exact age and locality cannot be determined from the image.
Uses & applications
Used as crushed aggregate, roadstone, building stone, riprap, and occasionally as a polished decorative stone or lapidary material.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust, including mid-ocean ridges and many ocean-island volcanoes.
Field identification & locations
Identify it by its very dark color, heavy feel, fine texture, and lack of visible large crystals; a streak test is typically gray-black, and a magnet may show weak attraction if iron-bearing minerals are abundant. Common worldwide in volcanic regions.
