igneous
Polished basalt pebble (likely basalt with quartz/zeolite veins)
Basalt; mainly calcic plagioclase and pyroxene, with possible alteration minerals such as quartz, calcite, or zeolites
AI-generated identification · may be incorrectFine-grained, dark gray to black, with subdued vitreous-to-waxy luster and thin pale vein patterns; typically Mohs 5–6, massive, with no visible cleavage and specific gravity about 2.8–3.0.
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Physical properties
Fine-grained, dark gray to black, with subdued vitreous-to-waxy luster and thin pale vein patterns; typically Mohs 5–6, massive, with no visible cleavage and specific gravity about 2.8–3.0.
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Its exact age cannot be determined from the photograph; the pale veins likely formed later through fluid alteration.
Uses & applications
Used as crushed aggregate, paving stone, riprap, and decorative landscaping material; polished pebbles are mainly sold for collecting or décor.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly develops rounded surfaces through river or beach abrasion. Pale veins can distinguish altered basalt from uniformly black glassy rocks such as obsidian.
Field identification & locations
Identify it by its dense black fine-grained texture, lack of vesicles, and heavy feel; a streak test is usually gray, and it is generally not scratched by a steel knife. Common in volcanic regions, river gravels, and coastal beaches.
