metamorphic
Rounded river cobble, likely quartzite
Quartzite (dominantly SiO₂); identification is tentative from the photograph
AI-generated identification · may be incorrectSmooth, water-worn, rounded surface; gray-brown with a pinkish patch and small pits, and a dull to slightly granular luster. Quartzite is typically Mohs 7, with interlocking quartz grains and no prominent cleavage; density is about 2.6–2.7 g/cm³.
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Physical properties
Smooth, water-worn, rounded surface; gray-brown with a pinkish patch and small pits, and a dull to slightly granular luster. Quartzite is typically Mohs 7, with interlocking quartz grains and no prominent cleavage; density is about 2.6–2.7 g/cm³.
Formation & geological history
Quartz-rich sandstone recrystallized under heat and pressure into quartzite, then rounded by transport in water. Its age and original location cannot be determined from the image.
Uses & applications
Quartzite is used as crushed aggregate, paving and building stone, and occasionally as a decorative or collectible specimen.
Geological facts
Quartzite can resemble quartz-rich sandstone, but its grains are fused during metamorphism and it generally resists scratching by a steel knife.
Field identification & locations
Look for a hard, compact rock with a sugary, interlocking quartz texture and no layering; this cobble’s smooth shape suggests stream or beach transport. Quartzite occurs worldwide in metamorphic belts.
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