igneous
Porphyritic rhyolite (likely lithophysal/vesicular rhyolite)
Rhyolite; chiefly quartz and alkali feldspar, with minor plagioclase and iron-bearing minerals
AI-generated identification · may be incorrectLight pink, cream, and gray with conspicuous cavities and crystal-rich patches; fine-grained to porphyritic, with a dull to slightly glassy luster. Hardness is about 6–7 Mohs; cleavage is absent overall, though feldspar crystals may cleave.
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Physical properties
Light pink, cream, and gray with conspicuous cavities and crystal-rich patches; fine-grained to porphyritic, with a dull to slightly glassy luster. Hardness is about 6–7 Mohs; cleavage is absent overall, though feldspar crystals may cleave.
Formation & geological history
An extrusive volcanic rock formed when silica-rich lava cooled rapidly, commonly producing vesicles or lithophysae from trapped gas. It may range from relatively young volcanic material to rocks hundreds of millions of years old, depending on locality.
Uses & applications
Used as decorative stone, aggregate, landscaping material, and occasionally as a lapidary specimen; attractive pieces have modest collector value.
Geological facts
Its pale pink coloration commonly reflects potassium feldspar, while cavities may later become lined or filled with quartz, zeolites, or other minerals.
Field identification & locations
Identify it by its pale felsic color, abundant quartz/feldspar-like grains, and volcanic cavities; distinguish it from granite by its generally finer groundmass. Common in volcanic regions such as the western United States, Mexico, Iceland, and New Zealand.
