igneous
Vesicular basalt (likely weathered volcanic rock)
Basalt, commonly composed of plagioclase, pyroxene, and olivine
AI-generated identification · may be incorrectLight tan, fine-grained, and highly vesicular with rounded cavities; fresh basalt is typically dark gray to black, but weathering can produce tan surfaces. Hardness about 6, generally dull to slightly glassy, with no visible cleavage; density is reduced by abundant pores.
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Physical properties
Light tan, fine-grained, and highly vesicular with rounded cavities; fresh basalt is typically dark gray to black, but weathering can produce tan surfaces. Hardness about 6, generally dull to slightly glassy, with no visible cleavage; density is reduced by abundant pores.
Formation & geological history
Forms when basaltic lava cools rapidly at or near the surface, trapping gas bubbles; the specimen’s age cannot be determined from the image and may range from ancient to recent.
Uses & applications
Used as aggregate, road stone, building stone, and occasionally as a decorative or collectible specimen; this porous piece has limited jewelry value.
Geological facts
The holes are vesicles, formed by escaping volcanic gases. Weathering and mineral staining can lighten basalt substantially.
Field identification & locations
Identify by its vesicles, fine texture, and lack of sedimentary layering; a streak test, hardness test, and examination of a fresh broken surface help distinguish it from porous limestone or pumice. Common worldwide in volcanic regions, including Hawaii, Iceland, India, and the Pacific Northwest.
