igneous
Vesicular basalt (possibly weathered lava rock)
Basalt; chiefly plagioclase, clinopyroxene, and olivine, with iron oxides
AI-generated identification · may be incorrectDark gray to tan, fine-grained, massive volcanic rock with weathered surfaces and small vesicles; dull to faintly vitreous luster, no visible cleavage, Mohs hardness about 5–6, specific gravity roughly 2.7–3.1.
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Physical properties
Dark gray to tan, fine-grained, massive volcanic rock with weathered surfaces and small vesicles; dull to faintly vitreous luster, no visible cleavage, Mohs hardness about 5–6, specific gravity roughly 2.7–3.1.
Formation & geological history
Forms when basaltic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows; age cannot be determined from the photograph and may range from recent to Precambrian.
Uses & applications
Used as crushed aggregate, road base, riprap, railway ballast, building stone, and landscaping material; ordinary pieces have little jewelry value.
Geological facts
The rounded shape and cavities are consistent with an eroded lava fragment or beach-worn volcanic cobble; the pale coating may represent weathering, mineral deposition, or surface alteration.
Field identification & locations
Identify by its fine texture, dark mafic minerals, heavy weight, and vesicles; common in volcanic regions such as Hawaii, Iceland, the Pacific Northwest, and oceanic islands. A specimen-scale photograph cannot confirm basalt versus another dark volcanic rock.
