metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or reddish-brown due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or reddish-brown due to iron oxide staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or reddish-brown due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together into a dense, hard mass. Found in mountain belts globally.
Uses & applications
Used as crushed stone for road construction and railway ballast. High-purity quartzite is used to produce glass, ferrosilicon, and silicon metal. Also used for decorative stone and countertops.
Geological facts
Quartzite is so tough that it often survives intense weathering better than surrounding rocks, frequently forming the peaks of mountain ranges. It is harder than steel and can easily scratch glass.
Field identification & locations
Identify by its extreme hardness and the fact that it breaks through the quartz grains rather than around them (unlike sandstone). Commonly found in Precambrian shield areas and Appalachian-style fold belts.
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