igneous
Likely basaltic/volcanic pebble
Fine-grained mafic volcanic rock, probably basalt (composition dominated by plagioclase and pyroxene)
AI-generated identification · may be incorrectGray, rounded water-worn pebble with dull to slightly waxy luster and granular texture; typically Mohs hardness 5–6, no obvious cleavage, and specific gravity about 2.8–3.1. The pale speckling may represent weathered feldspar or alteration minerals.
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Physical properties
Gray, rounded water-worn pebble with dull to slightly waxy luster and granular texture; typically Mohs hardness 5–6, no obvious cleavage, and specific gravity about 2.8–3.1. The pale speckling may represent weathered feldspar or alteration minerals.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in oceanic crust and volcanic fields. Its exact geological age cannot be determined from the photograph; the rounding indicates prolonged transport by water.
Uses & applications
Common basalt is used as aggregate, road stone, riprap, and landscaping material; attractive pieces may be collected, but this specimen has little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the ocean floor. Vesicles, if present, may later fill with zeolite, calcite, or quartz.
Field identification & locations
Identify it by its dark gray color, fine grain, substantial weight, and resistance to scratching with a steel nail; dilute acid should not fizz unless carbonate veins are present. Common worldwide, especially beaches, river gravels, and volcanic regions.
