igneous
Vesicular basalt (scoriaceous basalt)
Basalt, chiefly plagioclase feldspar and pyroxene with minor olivine; vesicles formed by trapped volcanic gas
AI-generated identification · may be incorrectHardness about 6; dark gray-black, fine-grained, dull to weakly vitreous luster, and abundant rounded to elongated vesicles. The pale flecks may be weathered feldspar, calcite, or surface infill; crystal structure is predominantly microscopic, with no prominent cleavage.
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Physical properties
Hardness about 6; dark gray-black, fine-grained, dull to weakly vitreous luster, and abundant rounded to elongated vesicles. The pale flecks may be weathered feldspar, calcite, or surface infill; crystal structure is predominantly microscopic, with no prominent cleavage.
Formation & geological history
An extrusive mafic igneous rock formed when low-viscosity basaltic lava cooled rapidly at or near the surface, preserving gas bubbles. It may range from recent lava to Precambrian in age, depending on locality.
Uses & applications
Used as lightweight aggregate, landscaping stone, drainage media, and occasionally in decorative specimens; generally not a jewelry material.
Geological facts
Its porous texture distinguishes scoria or vesicular basalt from dense basalt. A strongly glassy, extremely lightweight equivalent could instead be volcanic scoria or basaltic pumice.
Field identification & locations
Common in volcanic regions, including Hawaii, Iceland, the western United States, India, and oceanic islands. Check that vesicles are natural and the piece is not industrial slag; a streak, magnetism, and acid test on the pale material can help.
