igneous
Vesicular basalt (weathered volcanic rock)
Basalt, typically plagioclase + clinopyroxene ± olivine; cavities may contain secondary zeolite or calcite
AI-generated identification · may be incorrectDark brown to gray, fine-grained and dull, with rounded vesicles and a few pale mineral-filled cavities; hardness about 5–6, generally massive, with no obvious cleavage. The smooth shape suggests water-worn or tumbled material.
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Physical properties
Dark brown to gray, fine-grained and dull, with rounded vesicles and a few pale mineral-filled cavities; hardness about 5–6, generally massive, with no obvious cleavage. The smooth shape suggests water-worn or tumbled material.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; weathering and erosion later rounded it. Basalt ranges from Precambrian to modern, depending on its volcanic source.
Uses & applications
Used extensively as crushed aggregate, road base, building stone, and occasionally as decorative or lapidary material; this small specimen is mainly suitable for collecting.
Geological facts
Vesicles distinguish it from most dense volcanic rocks, while pale fillings commonly represent alteration minerals. Brown coloration likely reflects oxidation of iron-bearing minerals.
Field identification & locations
Identify by its fine texture, high density, dark iron-rich color, and rounded gas cavities; common near basaltic lava flows, volcanic islands, and river or beach gravels. A hand lens and streak, hardness, and magnetism tests can help confirm it.
