metamorphic
Quartzite Pebble
Quartzite (SiO2 composition)
Hardness 7 on Mohs scale; reddish-brown to brownish-tan color due to iron oxide staining; dull to sub-vitreous luster when wet; compact granular texture; tough and resistant to erosion.
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Physical properties
Hardness 7 on Mohs scale; reddish-brown to brownish-tan color due to iron oxide staining; dull to sub-vitreous luster when wet; compact granular texture; tough and resistant to erosion.
Formation & geological history
Formed when quartz-rich sandstone undergoes intense heat and pressure during regional metamorphism, fusing the quartz grains together into a dense, hard rock. Later eroded and rounded by stream or river action.
Uses & applications
Commonly used in landscape design, decorative stone features, road construction aggregate, and by lapidary hobbyists for tumbling.
Geological facts
Stream-rounded quartzite pebbles are among the toughest rocks found in riverbeds because the original quartz grains and quartz cement form an interlocking matrix that resists weathering far better than most other rock types.
Field identification & locations
Look for smooth, rounded pebbles along riverbanks, lakeshores, or gravel bars that cannot be scratched by a steel knife (hardness > 6.5) and break across grains rather than around them.
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