metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or yellowish with reddish iron staining; Luster: Vitreous to waxy; Crystal structure: Trigonal (hexagonal) system; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or yellowish with reddish iron staining
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or yellowish with reddish iron staining; Luster: Vitreous to waxy; Crystal structure: Trigonal (hexagonal) system; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse into a dense rock. Found in mountain belts and areas of tectonic activity.
Uses & applications
Used as aggregate in construction, road ballast, decorative stone in architecture, and as a source of silica in glassmaking.
Geological facts
Quartzite is so tough that it usually breaks through individual quartz grains rather than around them, which distinguishes it from sandstone.
Field identification & locations
Identify by its ability to scratch glass and its granular, crystalline texture. Commonly found in riverbeds, glacial deposits, or mountainous regions like the Appalachians or the Alps.
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