igneous
Vesicular basalt (scoria-like volcanic rock)
Basalt, typically composed of plagioclase feldspar, pyroxene, and minor olivine; vesicles may contain alteration minerals
AI-generated identification · may be incorrectDark reddish-brown, fine-grained, dull to slightly earthy luster, with small gas cavities and irregular fracture; hardness about 5–6, no obvious cleavage, specific gravity roughly 2.6–3.0 (lower if highly vesicular).
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Physical properties
Dark reddish-brown, fine-grained, dull to slightly earthy luster, with small gas cavities and irregular fracture; hardness about 5–6, no obvious cleavage, specific gravity roughly 2.6–3.0 (lower if highly vesicular).
Formation & geological history
An extrusive igneous rock formed when mafic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; commonly Cenozoic or younger, though basalt occurs throughout geologic time.
Uses & applications
Used as aggregate, road base, landscaping stone, and occasionally lightweight construction material; attractive scoria is collected but is generally low-value.
Geological facts
Its reddish-brown color commonly reflects oxidation of iron-bearing minerals during or after eruption. The specimen appears denser and finer-textured than typical highly vesicular scoria.
Field identification & locations
Identify by its dark mafic color, fine texture, lack of visible quartz, and vesicles; a streak, density, and fresh broken surface help distinguish it from brick or slag. Common in volcanic fields, lava flows, and cinder cones worldwide.
