metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Granular texture.
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Granular texture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic activity cause the quartz grains to recrystallize and fuse together.
Uses & applications
Used primarily in construction for decorative stone, road ballast, and roofing granules. Historically used for making stone tools.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in mountain ranges, forming prominent ridges and peaks. It is frequently mistaken for marble, but can be distinguished by its superior hardness.
Field identification & locations
Identify in the field by its ability to scratch glass and its grainy, sandpaper-like appearance under a lens. Common in metamorphic belts and as pebbles in riverbeds.
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