igneous
Likely vesicular basalt with weathering minerals
Basalt, primarily plagioclase and pyroxene, with possible iron oxides and secondary zeolite/carbonate minerals
AI-generated identification · may be incorrectDark gray to black, fine-grained and irregularly vesicular, with dull to locally sparkling surfaces and pale green-white weathering coatings. Hardness is approximately 5–6 Mohs; cleavage is not visible, and specific gravity is typically 2.8–3.0.
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Physical properties
Dark gray to black, fine-grained and irregularly vesicular, with dull to locally sparkling surfaces and pale green-white weathering coatings. Hardness is approximately 5–6 Mohs; cleavage is not visible, and specific gravity is typically 2.8–3.0.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. Its exact age cannot be determined from the image; pale coatings likely formed later through groundwater alteration.
Uses & applications
Commonly used as crushed aggregate, road stone, riprap, and building stone; attractive specimens are collected but have little gem value. Secondary zeolites or calcite may add collector interest.
Geological facts
The rough texture and dark color are consistent with basalt, but the specimen could also be an altered volcanic rock or slag without additional tests.
Field identification & locations
Look for a black fine-grained matrix, vesicles, a relatively high density, and a nonmetallic streak; a magnet may respond weakly if magnetite is present. Common worldwide, especially volcanic regions; estimated value is $2–$15 for a typical hand specimen, or $20–$75 if unusually mineralized.
