igneous
Weathered basaltic rock (probable basalt)
Basalt; fine-grained mafic volcanic rock, mainly plagioclase and pyroxene with possible olivine
AI-generated identification · may be incorrectDark gray-green, dull to weakly earthy luster, fine-grained and massive; typical hardness about 5–6 Mohs and specific gravity roughly 2.8–3.1. The image suggests weathering and possible vesicles or pits, but texture is insufficient for a definitive identification.
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Physical properties
Dark gray-green, dull to weakly earthy luster, fine-grained and massive; typical hardness about 5–6 Mohs and specific gravity roughly 2.8–3.1. The image suggests weathering and possible vesicles or pits, but texture is insufficient for a definitive identification.
Formation & geological history
Forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly from volcanic flows; specimens may range from geologically young to billions of years old. Brown-green surfaces commonly reflect oxidation and clay formation during weathering.
Uses & applications
Used extensively as crushed aggregate, road base, riprap, railway ballast, and dimension stone; attractive polished varieties may be used decoratively. This small weathered piece has little commercial or jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. It can be magnetic if it contains magnetite.
Field identification & locations
Common in volcanic regions, oceanic crust, flood-basalt provinces, and glacial deposits. Identify it by its dark color, heavy feel, fine grain, and lack of visible large crystals; a streak, magnet, and fresh broken surface would improve confidence.
