igneous
Tumbled quartz-rich pebble
Likely milky quartz with a dark mafic inclusion or attached basalt; exact identification requires testing
AI-generated identification · may be incorrectHardness about 7 for quartz (dark portion may be 5–6), white translucent color with gray-black granular zoning, vitreous to dull luster, no obvious cleavage, and irregular massive texture. The smooth shape indicates natural water wear or tumbling.
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Physical properties
Hardness about 7 for quartz (dark portion may be 5–6), white translucent color with gray-black granular zoning, vitreous to dull luster, no obvious cleavage, and irregular massive texture. The smooth shape indicates natural water wear or tumbling.
Formation & geological history
Likely derived from weathered quartz vein material or quartz-bearing igneous rock, with the dark area representing basalt, amphibolite, or biotite-rich material. Such rocks commonly formed in Precambrian to younger continental crust and were later rounded in streams or beaches.
Uses & applications
Primarily a decorative, lapidary, or collecting specimen; quartz-rich pebbles have limited industrial value compared with clean quartz deposits.
Geological facts
The pale portion should scratch ordinary glass, while the dark portion may not. A streak test, hardness testing, and close examination of the boundary can distinguish an attached rock fragment from mineral zoning.
Field identification & locations
Common in stream gravels, beaches, glacial deposits, and quartz-vein terrains worldwide; look for glass-scratching hardness and granular interlocking crystals. It is not identifiable as a specific named rock from the photograph alone.
