igneous
Basalt fragment
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to black, dull to weakly vitreous, typically dense and fine-grained; hardness about 5–6 Mohs, with no visible cleavage in the whole rock and irregular fracture. The specimen appears angular, weathered, and possibly vesicular or glassy, though the image limits certainty.
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Physical properties
Dark gray to black, dull to weakly vitreous, typically dense and fine-grained; hardness about 5–6 Mohs, with no visible cleavage in the whole rock and irregular fracture. The specimen appears angular, weathered, and possibly vesicular or glassy, though the image limits certainty.
Formation & geological history
Forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, lava flows, and volcanic islands. Basalt ranges from ancient Archean rocks to active eruptions today.
Uses & applications
Used widely as crushed aggregate, road base, railway ballast, asphalt material, and building stone; attractive polished basalt is also used decoratively. This small fragment has negligible commercial value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Its dark color reflects abundant ferromagnesian minerals and relatively low silica content.
Field identification & locations
Identify it by its black, compact appearance, fine texture, and relatively heavy weight; a streak, magnetism test, and fresh surface help distinguish it from coal or slag. Common worldwide, especially volcanic regions and oceanic terrains.
