metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, occasionally pink or reddish; Luster: vitreous (glassy) to dull; Crystal structure: hexagonal/trigonal silicate; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, occasionally pink or reddish
- Luster
- vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, occasionally pink or reddish; Luster: vitreous (glassy) to dull; Crystal structure: hexagonal/trigonal silicate; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. High heat and pressure reciprocal to tectonic plate movement cause sand grains to recrystallize and fuse together, obliterating previous sedimentary structures.
Uses & applications
Used as decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the production of glass and industrial silica.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it resists erosion much better than surrounding softer rocks.
Field identification & locations
Identify in the field by its superior hardness (it will easily scratch glass) and its sugary, crystalline texture where it breaks through grains rather than around them. Commonly found in folded mountain belts like the Appalachians.
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