igneous
Banded basalt pebble
Basalt, likely crossed by a pale quartz or calcite vein
AI-generated identification · may be incorrectFine-grained, dark gray, and typically dull to slightly glassy; mainly plagioclase and pyroxene, with possible olivine. Hardness is about 5–6 for basalt, while the white vein may be quartz (Mohs 7) or calcite (Mohs 3), and the specimen has no obvious cleavage.
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Physical properties
Fine-grained, dark gray, and typically dull to slightly glassy; mainly plagioclase and pyroxene, with possible olivine. Hardness is about 5–6 for basalt, while the white vein may be quartz (Mohs 7) or calcite (Mohs 3), and the specimen has no obvious cleavage.
Formation & geological history
Basalt forms from rapidly cooled mafic lava, generally in volcanic or oceanic settings; the pale band is a later mineral-filled fracture. Its exact geological age cannot be determined from the photograph.
Uses & applications
Common basalt is used as aggregate, roadstone, riprap, and building stone; attractive polished pebbles are used decoratively. This small beach-worn specimen has minimal commercial value.
Geological facts
The rounded shape and smooth surface indicate water abrasion. A vinegar test that bubbles on the white band suggests calcite; no reaction suggests quartz or another silicate.
Field identification & locations
Commonly found on volcanic shorelines, riverbeds, and basalt-rich glacial deposits. Identify it by its dark, dense fine-grained matrix and contrasting straight vein; a hand lens and streak, hardness, or acid tests can refine identification.
