metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often stained brown, pink, or yellow by iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (internal/microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often stained brown, pink, or yellow by iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (internal/microcrystalline); Cleavage: none (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 sand grains to recrystallize and fuse together into a dense, crystalline mass. It can be found in mountain belts and Precambrian shields.
Uses & applications
Used in construction as road ballast, gravel, and railway ballast; in industry as a source of silica for glass and silicon metal; and as decorative stone for counter tops, floor tiles, and fireplace surroundings.
Geological facts
Quartzite is so tough and durable that it often remains as high peaks and ridges after surrounding softer rocks have eroded away. It is often confused with marble, but can be distinguished because quartzite will scratch glass and marble will not.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, crystalline appearance on fresh surfaces. Unlike sandstone, when broken, quartzite fractures through the quartz grains rather than around them. Found globally in locations like the Appalachians and the Alps.
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