igneous
Polished rhyolite (likely porphyritic rhyolite)
Rhyolite, composed chiefly of quartz and alkali feldspar with minor plagioclase, biotite, and iron oxides
AI-generated identification · may be incorrectFine-grained volcanic rock with pink, salmon, cream, and gray mottling; likely porphyritic, with a dull to satin polish. Hardness is about 6–7 Mohs, with no prominent cleavage and specific gravity around 2.4–2.7.
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Physical properties
Fine-grained volcanic rock with pink, salmon, cream, and gray mottling; likely porphyritic, with a dull to satin polish. Hardness is about 6–7 Mohs, with no prominent cleavage and specific gravity around 2.4–2.7.
Formation & geological history
Formed when silica-rich lava cooled rapidly at or near Earth’s surface, commonly in volcanic domes and flows. Its exact age cannot be determined from the photograph; rhyolite occurs from Precambrian rocks to modern volcanic settings.
Uses & applications
Used as decorative stone, cabochons, worry stones, and lapidary material; massive rhyolite is also used locally for aggregate and building stone.
Geological facts
The red coloration commonly comes from hematite or other iron oxides, while pale patches may represent feldspar-rich zones or altered volcanic material.
Field identification & locations
Identify it by its very fine volcanic texture, light overall color, irregular flow or breccia-like pattern, and lack of visible large crystals; a streak, hardness, and magnification test would help distinguish it from jasper or granite. Common localities include the western United States, Mexico, Iceland, and volcanic regions worldwide.
