igneous
Vesicular basalt (likely iron-oxidized basalt)
Basalt; mainly plagioclase feldspar, pyroxene, and often olivine, with iron-oxide alteration
AI-generated identification · may be incorrectDark reddish-brown, fine-grained, dull to locally glassy luster, with abundant small vesicles and no visible cleavage; hardness about 5–6 Mohs, specific gravity roughly 2.8–3.0. The red color likely reflects hematite/goethite staining or weathering.
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Physical properties
Dark reddish-brown, fine-grained, dull to locally glassy luster, with abundant small vesicles and no visible cleavage; hardness about 5–6 Mohs, specific gravity roughly 2.8–3.0. The red color likely reflects hematite/goethite staining or weathering.
Formation & geological history
Extrusive mafic lava that cooled rapidly at or near Earth’s surface, trapping gas bubbles; commonly Cenozoic to Precambrian in age depending on locality. The surface appears strongly weathered or oxidized.
Uses & applications
Used as crushed aggregate, road stone, riprap, landscaping rock, and occasionally as a decorative specimen; generally not a jewelry gemstone.
Geological facts
Vesicles are gas cavities formed during eruption, while the iron-rich minerals oxidize to red-brown iron oxides. A magnetic response may occur if magnetite is present.
Field identification & locations
Identify by its heavy, fine-grained texture, reddish weathering rind, irregular vesicles, and possible weak magnetism; common in volcanic regions worldwide, including Hawaii, Iceland, India, and the western United States.
