igneous
Red porphyritic volcanic rock, likely rhyolite or andesite
Porphyritic rhyolite/andesite; composition appears quartz–feldspar with iron-oxide staining
AI-generated identification · may be incorrectHardness about 6–7 Mohs; pink-red, gray, and black colors; dull to slightly vitreous luster; fine-grained groundmass containing larger pale and dark crystals; no obvious cleavage. The granular surface may include weathered phenocrysts and vesicles.
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Physical properties
Hardness about 6–7 Mohs; pink-red, gray, and black colors; dull to slightly vitreous luster; fine-grained groundmass containing larger pale and dark crystals; no obvious cleavage. The granular surface may include weathered phenocrysts and vesicles.
Formation & geological history
An extrusive igneous rock formed when silica-rich to intermediate lava cooled at or near Earth’s surface, producing visible phenocrysts in a finer matrix. Its exact age cannot be determined from the photograph and depends on locality.
Uses & applications
Used locally as building or landscaping stone, aggregate, and lapidary material; attractive pieces may be polished, though this specimen appears ordinary rather than gem-grade.
Geological facts
The red coloration commonly results from oxidation of iron-bearing minerals. Distinguishing rhyolite from andesite requires mineral identification or chemical analysis, especially where weathering obscures texture.
Field identification & locations
Look for a fine volcanic matrix with larger feldspar, quartz, or dark mineral crystals; a streak test, hand lens, and hardness test help, while a geological map can establish locality. Common worldwide in volcanic belts, including the western United States, Mexico, Andes, and Japan.
