metamorphic
Quartzite river stone
Quartzite (SiO2 silicon dioxide)
Hardness: 7 on Mohs scale; Color: tan, light grey, or off-white; Luster: dull to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: approx 2.65
- Hardness
- 7 on Mohs scale
- Color
- tan, light grey, or off-white
- Luster
- dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, light grey, or off-white; Luster: dull to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: approx 2.65
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism). Usually found in riverbeds or beaches where water has smoothed and rounded the specimen over many years.
Uses & applications
Used in construction for road ballast, as decorative gravel in landscaping, and in the manufacturing of glass and ceramics. Smooth specimen are popular for painting and meditation tools.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is more resistant to weathering than its parent rock, sandstone, which is why it often persists as rounded cobbles in river systems.
Field identification & locations
Identify by its high hardness (cannot be scratched by a steel nail) and grainy, sugary texture visible under a loupe. Commonly found in areas with ancient mountain belts or glacial till.
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