igneous
Weathered vesicular basalt (likely amygdaloidal basalt)
Basalt, composed mainly of plagioclase feldspar, pyroxene, and altered olivine; cavities may contain secondary zeolite, calcite, or silica
AI-generated identification · may be incorrectDark brown-gray, fine-grained, dull to slightly earthy luster, with numerous rounded vesicles and weathered iron-oxide staining; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The pale patches may be alteration minerals or surface weathering.
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Physical properties
Dark brown-gray, fine-grained, dull to slightly earthy luster, with numerous rounded vesicles and weathered iron-oxide staining; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The pale patches may be alteration minerals or surface weathering.
Formation & geological history
An extrusive volcanic rock formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; later groundwater alteration and oxidation produced the brown coloration. Basalt ranges from Precambrian to modern age.
Uses & applications
Commonly used as crushed aggregate, road material, riprap, and building stone; attractive polished pieces are collected, though this specimen has limited gem value.
Geological facts
Its holes are vesicles, distinguishing volcanic basalt from most sedimentary rocks; mineral-filled vesicles would make it specifically amygdaloidal basalt.
Field identification & locations
Identify by its dense, fine-grained body, vesicles, high density, and lack of visible sand grains or fossils; common worldwide in volcanic regions, including Hawaii, Iceland, India, and oceanic crust.
