igneous
Weathered basalt (likely vesicular basalt)
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to brown, fine-grained, with scattered pale mineral or weathering patches; typically dull to slightly glassy, hardness about 5–6, dense, and lacking visible cleavage. The specimen appears strongly weathered and may contain small vesicles or altered inclusions.
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Physical properties
Dark gray to brown, fine-grained, with scattered pale mineral or weathering patches; typically dull to slightly glassy, hardness about 5–6, dense, and lacking visible cleavage. The specimen appears strongly weathered and may contain small vesicles or altered inclusions.
Formation & geological history
An extrusive mafic igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions. Its exact age cannot be determined from the photograph; basalt forms from Precambrian to modern times.
Uses & applications
Used extensively as crushed aggregate, road base, paving stone, riprap, and building stone; attractive polished varieties can be used decoratively, but this fragment has little jewelry value.
Geological facts
Basalt is the most common volcanic rock and makes up much of the oceanic crust. Weathering can produce rusty brown surfaces through oxidation of iron-bearing minerals.
Field identification & locations
Commonly identified by its dark color, fine texture, high density, and absence of large crystals; a hand lens, streak, and fresh broken surface would improve identification. Common worldwide, especially volcanic regions and ocean floors.
