metamorphic
Quartzite
Quartzite (principally SiO2)
Hardness: 7 on Mohs scale; Color: Tan to yellowish-white; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan to yellowish-white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to yellowish-white; 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 sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The original quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop surfaces. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and glass.
Geological facts
Quartzite is so tough that it often outlasts the rocks surrounding it, forming prominent ridges and hills. It is often confused with marble, but unlike marble, it will not fizz when in contact with acid.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that has been fused into a crystalline mass. Commonly found in folded mountain ranges worldwide.
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