metamorphic
Rounded quartz-rich cobble
Likely quartzite, composed chiefly of SiO₂ (quartz); exact identification is uncertain from the image
AI-generated identification · may be incorrectTan to cream, dull weathered surface, massive and rounded with no obvious cleavage or visible crystals. If quartzite, hardness is about 7 Mohs and specific gravity about 2.6–2.7.
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Physical properties
Tan to cream, dull weathered surface, massive and rounded with no obvious cleavage or visible crystals. If quartzite, hardness is about 7 Mohs and specific gravity about 2.6–2.7.
Formation & geological history
Quartzite forms when quartz sandstone is recrystallized by heat and pressure; its age depends on the source rock and regional metamorphism. The rounded shape likely resulted from transport and abrasion in a stream or along a shore.
Uses & applications
Commonly used as decorative landscaping stone, aggregate, and building stone; this cobble appears mainly suitable for collecting or decoration.
Geological facts
Quartzite is harder than the sandstone from which it forms, and usually resists scratching by a steel knife.
Field identification & locations
Look for a hard, interlocking quartz texture and grains that do not rub off; a glass scratch test can help distinguish it from softer sandstone, but the pictured surface alone cannot confirm quartzite. Rounded cobbles occur in river, beach, and glacial deposits.
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