igneous
Weathered volcanic rock, likely altered basalt
Altered basalt (fine-grained mafic volcanic rock; exact identification requires testing)
AI-generated identification · may be incorrectTypically Mohs 5–6, dull earthy luster, pale yellow-green weathering rind, and fine-grained massive texture; the coloration may reflect chlorite, epidote, zeolites, or iron staining. No visible crystals or cleavage are apparent.
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Physical properties
Typically Mohs 5–6, dull earthy luster, pale yellow-green weathering rind, and fine-grained massive texture; the coloration may reflect chlorite, epidote, zeolites, or iron staining. No visible crystals or cleavage are apparent.
Formation & geological history
Basalt forms when basaltic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields or oceanic crust; this specimen appears strongly weathered or hydrothermally altered. Its precise age cannot be determined from the image.
Uses & applications
Ordinary basalt is used as crushed aggregate, roadstone, riprap, and building stone; attractive altered pieces may be collected, but this specimen has little commercial value.
Geological facts
The yellow-green surface likely results from chemical alteration rather than the rock’s original color. A fresh broken surface would be more diagnostic than the weathered exterior.
Field identification & locations
Common in volcanic regions and glacially transported gravels. Test for hardness, streak, density, magnetism, and acid reaction; a hand lens may reveal tiny feldspar or pyroxene crystals.
