metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or reddish due to iron oxides; Luster: vitreous to grainy; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.64-2.69
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or reddish due to iron oxides
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or reddish due to iron oxides; Luster: vitreous to grainy; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.64-2.69
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together into a dense, hard rock. Often formed during mountain-building events in various geological eras.
Uses & applications
Used in construction for road ballast, floor tiles, and wall coverings. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics. Some colorful varieties are used as ornamental stones.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges in which it formed, frequently appearing on ridges and hilltops because it is highly resistant to chemical and physical weathering.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its grainy, sugary appearance on a fresh break. Commonly found in folded mountain belts like the Appalachians or the Alps.
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