metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often tan or yellowish due to iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (cryptocrystalline); Cleavage: none; 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 tan or yellowish due to iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (cryptocrystalline); Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, where quartz grains recrystallize and fuse together into a dense mass. Found in mountain ranges or deep within the crust.
Uses & applications
Used in construction for road ballast, roofing granules, and as a dimension stone for flooring and wall facings. Due to its hardness, it is also used for abrasive purposes.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountains because it withstands erosion much better than the rocks surrounding it.
Field identification & locations
Identified by its extreme hardness (it will easily scratch glass) and its grainy, sandpaper-like surface that does not break around grains but through them. Frequently found in metamorphic belts worldwide.
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