metamorphic
Quartzite cobble (probable)
Quartzite, composed predominantly of recrystallized quartz (SiO₂)
AI-generated identification · may be incorrectGray to tan, dull-to-glassy granular surface; quartz has Mohs hardness 7 and no cleavage. The rounded shape and weathered surface make identification from the image uncertain.
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Physical properties
Gray to tan, dull-to-glassy granular surface; quartz has Mohs hardness 7 and no cleavage. The rounded shape and weathered surface make identification from the image uncertain.
Formation & geological history
Forms when quartz-rich sandstone is buried and recrystallized by heat and pressure, typically during mountain-building; age depends on its source rock and cannot be determined from appearance alone.
Uses & applications
Commonly used as construction aggregate, paving and landscaping stone; attractive pieces may be collected or used decoratively.
Geological facts
Quartzite is very hard and resists weathering; a fresh broken surface often shows tightly fused quartz grains.
Field identification & locations
Look for a hard, quartz-rich rock that scratches glass and breaks through grains rather than around them. Quartzite occurs worldwide in metamorphic mountain belts; this rounded cobble may have been transported by a river or glacier.
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