metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or yellow/tan due to iron oxidation; Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or yellow/tan due to iron oxidation
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or yellow/tan due to iron oxidation; Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse into a dense, interlocking matrix.
Uses & applications
Used as a decorative building stone, road ballast, railroad ballast, and in the production of glass and industrial abrasives. High-purity quartzite is used in the metallurgical and chemical industries.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and hills. It is often confused with marble, but can be distinguished because quartzite will scratch glass while marble will not.
Field identification & locations
Look for a sugary, crystalline texture and a fracture that breaks across the individual sand grains rather than around them. It is commonly found in mountain ranges like the Appalachians, the Alps, and the Himalayas.
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