igneous
Weathered basaltic river pebble
Basalt, likely altered or partially vesicular basalt
AI-generated identification · may be incorrectFine-grained, dark gray-brown rock with tan weathering and scattered pale mineral patches; typically nonmetallic and dull, with hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The rounded shape indicates water abrasion.
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Physical properties
Fine-grained, dark gray-brown rock with tan weathering and scattered pale mineral patches; typically nonmetallic and dull, with hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The rounded shape indicates water abrasion.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at Earth’s surface, commonly in volcanic fields or oceanic crust; the specimen was later weathered and transported by water. Basalt is generally Phanerozoic or younger, but its exact age cannot be determined from the image.
Uses & applications
Common basalt is used as crushed aggregate, road base, riprap, and occasionally building stone; this small weathered pebble has little commercial or jewelry value.
Geological facts
The pale areas may be feldspar, zeolite, or secondary alteration minerals filling former pores. Brown coloration likely reflects oxidation of iron-bearing minerals.
Field identification & locations
Identify basalt by its fine grain, dark color, heavy feel, and lack of visible large crystals; a streak, magnetism test, and fresh fracture would improve identification. Common worldwide, especially volcanic regions and river gravels.
