metamorphic
Rounded quartzite cobble
Quartzite, composed predominantly of recrystallized quartz (SiO₂)
AI-generated identification · may be incorrectPale tan-gray with rusty iron staining and a fine-grained, granular surface; quartz has Mohs hardness 7 and vitreous luster, though this specimen’s texture appears weathered. Quartzite is typically massive, with no prominent cleavage and specific gravity around 2.6–2.7.
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Physical properties
Pale tan-gray with rusty iron staining and a fine-grained, granular surface; quartz has Mohs hardness 7 and vitreous luster, though this specimen’s texture appears weathered. Quartzite is typically massive, with no prominent cleavage and specific gravity around 2.6–2.7.
Formation & geological history
Forms when quartz-rich sandstone is recrystallized under heat and pressure, commonly during regional metamorphism; the specimen’s age cannot be determined from the image. Its rounded shape likely reflects prolonged transport or abrasion in a river or beach environment.
Uses & applications
Quartzite is used as crushed stone, road aggregate, building and decorative stone, and occasionally as a source of silica; this cobble is mainly a collector or display piece.
Geological facts
Quartzite can be deceptively similar to quartz-rich sandstone, but its interlocking quartz grains make it notably hard and resistant to abrasion.
Field identification & locations
Look for a hard, sugary or fused-looking texture; quartzite commonly scratches glass and does not fizz in dilute acid. Quartz-rich quartzite occurs worldwide, often in metamorphic mountain belts and as river or beach cobbles.
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