igneous
Weathered porphyritic volcanic rock (possibly andesite)
Likely porphyritic andesite; exact identification requires closer examination
AI-generated identification · may be incorrectDull, mottled gray-brown, fine-grained groundmass with possible small crystals; likely plagioclase with minor dark minerals. Approximate Mohs hardness 6; crystal structure is fine-grained and not readily visible.
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Physical properties
Dull, mottled gray-brown, fine-grained groundmass with possible small crystals; likely plagioclase with minor dark minerals. Approximate Mohs hardness 6; crystal structure is fine-grained and not readily visible.
Formation & geological history
Formed when intermediate-composition lava cooled at or near Earth’s surface, leaving larger crystals in a finer groundmass; its age cannot be determined from the image.
Uses & applications
Primarily a geological or collector specimen; andesite is also used locally as crushed aggregate and building stone.
Geological facts
Porphyritic texture records two-stage cooling: crystals grew slowly before the remaining magma cooled more rapidly.
Field identification & locations
The hand-sized, rounded specimen appears weathered and lacks clear diagnostic features, so andesite is tentative; compare crystal texture and test hardness, or consult a geologist. Andesite occurs in volcanic arcs worldwide.
