metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, can be pink 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
- typically white to gray, can be pink or reddish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, can be pink 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 or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. Most deposits date from the Precambrian to Paleozoic eras.
Uses & applications
Used as a decorative stone in construction, for kitchen countertops (as 'natural quartzite'), railway ballast, and as a source of silica for glass manufacturing.
Geological facts
Quartzite is so hard that it will scratch glass and steel. Unlike sandstone, which breaks around its grains, quartzite breaks through its grains due to the complete recrystallization of the quartz.
Field identification & locations
Identify in the field by its extreme hardness and sugary, crystalline texture on fresh breaks. It is often found in folded mountain belts. Common in the Appalachian Mountains, Brazil, and Scandinavia.
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