igneous
Vesicular basalt (weathered volcanic rock)
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine, with iron oxides
AI-generated identification · may be incorrectTypically dark gray to brown, fine-grained, and dull to subtly vitreous; abundant gas vesicles are visible, some lined with secondary minerals. Hardness is about 5–6 Mohs, with no obvious cleavage and specific gravity commonly 2.7–3.1.
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Physical properties
Typically dark gray to brown, fine-grained, and dull to subtly vitreous; abundant gas vesicles are visible, some lined with secondary minerals. Hardness is about 5–6 Mohs, with no obvious cleavage and specific gravity commonly 2.7–3.1.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping volcanic gas bubbles; its exact age cannot be determined from the image and may range from recent volcanic material to ancient basalt.
Uses & applications
Used as crushed aggregate, road base, riprap, and occasionally building stone; vesicular pieces are mainly collected as volcanic specimens rather than used in jewelry.
Geological facts
The holes are vesicles, not fossil cavities; weathering can produce the rusty brown coloration by oxidizing iron-bearing minerals. A magnetic response is common but variable.
Field identification & locations
Common in volcanic regions, including Hawaii, Iceland, the Pacific Northwest, India’s Deccan Traps, and oceanic crust. Identify it by its fine dark matrix, vesicles, heavy feel, and possible weak magnetism; confirm with a fresh broken surface.
