igneous
Weathered mafic rock fragment
Likely basalt or volcanic breccia; identification is uncertain from the photograph
AI-generated identification · may be incorrectDark gray to black, fine-grained and irregular, with tan/yellow weathering products and scattered pale mineral grains. Likely Mohs hardness 5–6, dull to weakly vitreous luster, massive texture, and no obvious cleavage; density approximately 2.7–3.1 g/cm³.
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Physical properties
Dark gray to black, fine-grained and irregular, with tan/yellow weathering products and scattered pale mineral grains. Likely Mohs hardness 5–6, dull to weakly vitreous luster, massive texture, and no obvious cleavage; density approximately 2.7–3.1 g/cm³.
Formation & geological history
Probably an igneous volcanic fragment formed from rapidly cooled mafic lava or pyroclastic material, potentially millions to billions of years old depending on locality. Surface alteration has produced the yellow-brown patches.
Uses & applications
Common basalt is used as aggregate, road stone, riprap, and occasionally stonework; small unexceptional fragments have little commercial or jewelry value.
Geological facts
The pale grains may be feldspar, while yellow-brown areas could be iron-oxide/clay alteration or weathered sulfide minerals. A fresh broken surface and a streak, magnetism, and acid tests would improve identification.
Field identification & locations
Look for a dark, dense, fine-grained matrix and tiny feldspar or pyroxene crystals; basalt commonly occurs in lava flows, volcanic fields, and oceanic crust. Estimated value: $0–$5 as an ordinary fragment, or $5–$20 if locality-proven or visually distinctive.
