igneous
Vesicular basalt (possibly slag-like volcanic rock)
Basalt, predominantly plagioclase–pyroxene–olivine; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectDark gray-black, fine-grained, very dense, with rounded vesicles and a dull to weakly vitreous luster; typical basalt hardness is about Mohs 6, with irregular fracture and no obvious cleavage. Pale crystalline patches may be feldspar, quartz, or secondary minerals.
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Physical properties
Dark gray-black, fine-grained, very dense, with rounded vesicles and a dull to weakly vitreous luster; typical basalt hardness is about Mohs 6, with irregular fracture and no obvious cleavage. Pale crystalline patches may be feldspar, quartz, or secondary minerals.
Formation & geological history
Likely formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; basalt commonly ranges from Precambrian to modern age. The rounded, highly bubbled appearance could alternatively indicate industrial iron/steel slag, which requires testing to exclude.
Uses & applications
Basalt is used as crushed aggregate, road stone, building stone, and occasionally as a decorative material; slag has mainly industrial and educational interest. This specimen has little jewelry value unless confirmed as an unusual locality specimen.
Geological facts
Basalt is the most abundant volcanic rock in Earth’s oceanic crust. Vesicles may later fill with zeolite, calcite, quartz, or amethyst, producing amygdaloidal basalt.
Field identification & locations
Check for a natural fine-grained matrix, mineral-filled vesicles, and absence of metallic droplets or flow-glass textures; a streak, magnet, density, and acid test can help distinguish basalt from slag. Common worldwide, especially volcanic regions.
