metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: Brownish-red to purple-grey; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (fractures across grains); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Brownish-red to purple-grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Brownish-red to purple-grey; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (fractures across grains); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure Recrystallize quartz grains into a dense, interlocking mosaic. Often Precambrian to Paleozoic in age.
Uses & applications
Used as crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics due to high silica content. Occasionally used as decorative garden stone.
Geological facts
Quartzite is so tough that it often survives erosion better than any other rock type, frequently forming the caps of mountains or ridgelines. This specific specimen shows 'desert varnish' or water-smoothed edges from alluvial transport.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and the way it breaks through sand grains rather than around them. Commonly found in riverbeds and glacial tills across North America.
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