metamorphic
Tumbled gray pebble, likely quartzite or fine-grained quartz-rich rock
Quartzite (probable), composed mainly of quartz (SiO₂)
AI-generated identification · may be incorrectSmooth, rounded, gray-brown, opaque to slightly translucent pebble with a dull-to-subvitreous luster; quartz hardness is about 7 Mohs, with no obvious cleavage and conchoidal-to-granular fracture. Exact identification is limited by the polished/tumbled surface and photograph.
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Physical properties
Smooth, rounded, gray-brown, opaque to slightly translucent pebble with a dull-to-subvitreous luster; quartz hardness is about 7 Mohs, with no obvious cleavage and conchoidal-to-granular fracture. Exact identification is limited by the polished/tumbled surface and photograph.
Formation & geological history
Likely formed when quartz-rich sandstone was metamorphosed and recrystallized during mountain-building, commonly millions to billions of years ago. It may have been naturally water-rounded or mechanically tumbled.
Uses & applications
Used as decorative stone, landscaping gravel, aquarium material, and lapidary/tumbled-stone specimens; quartzite is also used as durable aggregate and building stone.
Geological facts
Quartzite commonly resists weathering better than surrounding rocks, forming resistant ridges and rounded stream pebbles. A steel file should not scratch it, while quartzite can scratch ordinary glass.
Field identification & locations
Look for uniform granular texture, strong resistance to scratching, and absence of visible cleavage; acid produces no reaction. Common worldwide in metamorphic belts and river gravels.
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