metamorphic
Quartzite (River Pebble)
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale), Color: Brownish-tan with orange iron staining, Luster: Dull to waxy when wet, Crystal Structure: Granular/Microcrystalline, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-tan with orange iron staining, Luster: Dull to waxy when wet, Crystal Structure: Granular/Microcrystalline, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing quartz grains to recrystallize and fuse. This specimen has been rounded by fluvial (river) erosion.
Uses & applications
Construction aggregate, decorative landscaping, and occasionally used as a source for silica in glass making. Common as a lapidary material for tumbling.
Geological facts
Quartzite is one of the hardest and most durable common rocks on Earth, often surviving long after the softer surrounding rock has eroded away. Iron oxides frequently give it an orange or red tint.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that does not rub off. Commonly found in riverbeds and glacial deposits.
