metamorphic
Quartzite (River Pebble)
Crystalline Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white, grey, with tan/yellow iron staining; Luster: Vitreous when wet, waxy/dull when dry; Structure: Granular/Crystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Off-white, grey, with tan/yellow iron staining
- Luster
- Vitreous when wet, waxy/dull when dry
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white, grey, with tan/yellow iron staining; Luster: Vitreous when wet, waxy/dull when dry; Structure: Granular/Crystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure. The individual quartz grains recrystallize into a locked mosaic. This specific specimen has been further shaped by fluvial (river) erosion.
Uses & applications
Industrial use in glassmaking, abrasives, and as a refractory material. Used as high-durability construction aggregate and in landscaping. Rare, colorful, or translucent pieces are used in lapidary work.
Geological facts
Quartzite is so durable that it can survive surface weathering for millions of years. It is often tougher than the rocks that surround it, leading it to form prominent ridges or mountain caps.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and its granular, sugary texture on freshly broken surfaces. Found worldwide in riverbeds and glacial deposits.
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