metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or yellowish; 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 yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or yellowish; 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 under intense heat and pressure, typically during mountain-building events (orogeny). The individual quartz grains recrystallize into a locked mosaic.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a raw material in the glass and silicate industries. Polished slabs are used for countertops and flooring.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, 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 inability to be scratched by a steel knife and its sugary, granular texture on fresh surfaces. It is found globally in folded mountain belts and ancient shield areas.
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