igneous
Tumbled rhyolite (likely)
Rhyolite, a felsic volcanic rock composed mainly of quartz and alkali feldspar, with biotite or hornblende
AI-generated identification · may be incorrectPink, gray, and dark patches with a fine-grained texture and dull to slightly waxy luster; hardness about 6–7 Mohs, typically massive with no cleavage. The rounded shape indicates tumbling or water wear.
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Physical properties
Pink, gray, and dark patches with a fine-grained texture and dull to slightly waxy luster; hardness about 6–7 Mohs, typically massive with no cleavage. The rounded shape indicates tumbling or water wear.
Formation & geological history
Formed when silica-rich lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions; age depends on locality and may range from recent to Precambrian. Exact identification is limited by the photograph.
Uses & applications
Used as decorative stone, landscaping material, lapidary specimens, and occasionally aggregate or building stone. Common tumbled pieces generally have modest collector value.
Geological facts
The pink coloration commonly reflects potassium feldspar, while dark areas may contain biotite, hornblende, or volcanic glass. It may resemble granite, but rhyolite is generally much finer grained.
Field identification & locations
Look for a dense, fine-grained volcanic texture, pink feldspar, gray quartz, and dark mafic minerals; a hand lens or thin section can distinguish it from granite. Common in volcanic regions worldwide, including the western United States.
