metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, white, or reddish; 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, tan, white, or reddish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, white, or reddish; 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-rich sandstone under high heat and pressure, typically during mountain-building events. The original quartz sand grains recrystallize into an interlocking mosaic.
Uses & applications
Used as crushed stone for road construction and railroad ballast. High-quality varieties are used for kitchen countertops, flooring, wall cladding, and as decorative landscape boulders.
Geological facts
Quartzite is so tough that it often survives intense weathering better than surrounding rocks, frequently forming the tops of ridges and hills. It is often confused with marble, but unlike marble, quartzite will not react with acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline texture on fresh breaks. It is commonly found in ancient mountain belts such as the Appalachians and the Alps.
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