igneous
Black basalt (likely polished or cut fragment)
Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase, clinopyroxene, and often olivine or magnetite
AI-generated identification · may be incorrectDark gray to black, fine-grained, generally dull to slightly vitreous; hardness about 5–6 Mohs, no visible cleavage, and specific gravity roughly 2.8–3.0. The image shows a dense, angular, possibly textured or coated fragment with no diagnostic crystals visible.
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Physical properties
Dark gray to black, fine-grained, generally dull to slightly vitreous; hardness about 5–6 Mohs, no visible cleavage, and specific gravity roughly 2.8–3.0. The image shows a dense, angular, possibly textured or coated fragment with no diagnostic crystals visible.
Formation & geological history
Forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in oceanic crust, lava flows, and volcanic islands. Individual pieces may be geologically young or millions to billions of years old depending on source.
Uses & applications
Widely used as crushed aggregate, road stone, building stone, paving, countertops, and architectural cladding; attractive polished pieces are used decoratively but usually have modest collector value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and makes up much of the ocean floor. Magnetic basalt may contain magnetite and can record ancient geomagnetic field directions.
Field identification & locations
Identify it by its uniform dark color, fine texture, high density, and lack of large crystals; a streak, hardness, and magnetism test would help. Common worldwide, especially volcanic regions and oceanic terrains.
