metamorphic
Red Quartzite
Quartzite (primarily SiO2 with trace Fe2O3)
Hardness: 7 on Mohs scale; Color: Reddish-pink to brownish-orange (due to iron oxide); Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Reddish-pink to brownish-orange (due to iron oxide)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-pink to brownish-orange (due to iron oxide); Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. The red hue is caused by hematite or other iron mineral inclusions. Examples can range from Proterozoic to more recent geological ages.
Uses & applications
Used frequently in construction as road ballast, railway track ballast, and crushed stone. High-quality slabs are used for countertops, flooring, and decorative stone (dimension stone).
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming prominent ridges and hills. It is one of the hardest common rocks and will easily scratch glass and steel.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, crystalline texture that resembles sandpaper but feels smooth to the touch. Unlike sandstone, quartzite breaks through the quartz grains rather than around them. Common in the Sioux Quartzite formation of the US Midwest and various shields worldwide.
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