igneous
Weathered basalt (likely vesicular basalt)
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark brown-gray, fine-grained, dull to faintly earthy luster, with small weathering pits or vesicles; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The reddish-brown color likely reflects surface oxidation and weathering.
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Physical properties
Dark brown-gray, fine-grained, dull to faintly earthy luster, with small weathering pits or vesicles; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The reddish-brown color likely reflects surface oxidation and weathering.
Formation & geological history
An extrusive igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface; basalt commonly ranges from Precambrian to modern age. The rounded shape indicates prolonged transport or human tumbling/weathering.
Uses & applications
Used widely as crushed aggregate, road base, railway ballast, riprap, and building stone; attractive polished pieces are occasionally sold as curiosities. This specimen appears to have little commercial gem value.
Geological facts
Basalt is the most common volcanic rock and forms much of the oceanic crust, including mid-ocean ridges and many oceanic islands.
Field identification & locations
Identify it by its heavy feel, fine grain, dark color, and lack of visible large crystals; a steel file usually scratches it only with difficulty. Common worldwide, especially in volcanic regions; confirm with a fresh broken surface or streak-free hardness testing.
