igneous
Fine-grained volcanic rock, likely andesite
Andesite (intermediate-composition volcanic rock; identification from image is approximate)
AI-generated identification · may be incorrectGray to brown, dull, fine-grained and apparently massive, with no visible crystals; composed mainly of plagioclase with possible pyroxene or amphibole. Hardness is generally about 6 on the Mohs scale; crystal structure is too fine-grained to distinguish here.
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Physical properties
Gray to brown, dull, fine-grained and apparently massive, with no visible crystals; composed mainly of plagioclase with possible pyroxene or amphibole. Hardness is generally about 6 on the Mohs scale; crystal structure is too fine-grained to distinguish here.
Formation & geological history
Forms when intermediate-composition lava cools at or near Earth’s surface, commonly in volcanic arcs; its age cannot be determined from the image.
Uses & applications
Used locally as crushed aggregate and building stone; this small, ordinary fragment has little commercial value.
Geological facts
Andesite is named for the Andes, where it is widespread; fresh surfaces are typically more uniform than weathered ones.
Field identification & locations
Look for a compact, fine-grained gray rock, often with small pale feldspar crystals. Common around volcanic arcs; a hand specimen like this is typically worth about $0–$5.
