igneous
Rounded weathered rock, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; precise identification requires testing
AI-generated identification · may be incorrectDark gray-brown, dull to weakly earthy luster, fine-grained and rounded by abrasion; likely Mohs hardness 5–6, with no obvious cleavage. The pale patches may be weathering or feldspar minerals.
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Physical properties
Dark gray-brown, dull to weakly earthy luster, fine-grained and rounded by abrasion; likely Mohs hardness 5–6, with no obvious cleavage. The pale patches may be weathering or feldspar minerals.
Formation & geological history
Probably an erosion-rounded volcanic fragment formed when lava cooled rapidly at or near Earth’s surface; its exact geological age and source cannot be determined from the photograph.
Uses & applications
Commonly used as gravel, aggregate, landscaping stone, and occasionally as a hand specimen; little jewelry value unless unusually attractive or historically significant.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust, while andesite commonly forms at volcanic arcs above subduction zones.
Field identification & locations
Look for a dense, fine texture, lack of visible quartz, and a dark streak; basalt is typically weakly magnetic, whereas acid fizz suggests carbonate contamination. A fresh fracture, streak, magnet, and hardness test would improve identification; common worldwide.
