metamorphic
Quartzite
Quartzite (predominantly SiO2)
Hardness: 7 Mohs scale; Color: Reddish-pink to light brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 Mohs scale
- Color
- Reddish-pink to light brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Reddish-pink to light brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/conchoidal fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone under high heat and pressure, causing the original quartz grains to recrystallize and fuse together into a dense, hard mass.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop surfaces; also used as a gemstone when polished or as high-purity silica in industrial glassmaking.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of mountains and ridges, resisting erosion more effectively than the rocks around it. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its hardness (scratches glass) and its characteristic grainy 'sandpaper' appearance combined with a fused, crystalline texture. It is commonly found in mountain belts and glacial till.
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