metamorphic
Quartzite (River Pebble)
SiO2 (recrystallized Quartz)
Hardness: 7 on Mohs scale; Color: Tan to light grey; Luster: Dull to vitreous; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None; Specific gravity: ~2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan to light grey
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to light grey; Luster: Dull to vitreous; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None; Specific gravity: ~2.65.
Formation & geological history
Quartzite forms when quartz-rich sandstone is subjected to heat and pressure during regional metamorphism. This specific specimen has been rounded and smoothed through water erosion in a fluvial (river) or coastal environment.
Uses & applications
Used in construction as crushed stone, railway ballast, and occasionally for high-durability countertops. In this pebble form, it is often used for landscaping or decorative gravel.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of hills and ridges because it resists erosion better than the surrounding rock types.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its grainy, 'sugary' texture seen in fresh breaks. Found globally in ancient mountain belts and riverbeds.
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