metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often yellow or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with a conchoidal or irregular 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, gray, or tan, but often yellow or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with a conchoidal or irregular fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together. Most quartzite found in surface deposits dates from the Precambrian to Cenozoic eras.
Uses & applications
Extensively used in construction for road ballast, railway tracks, and industrial aggregate. High-quality slabs are used for countertops, flooring, and decorative facades. High-purity quartzite is also a source of silica for glassmaking.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming prominent ridges and hills. It is harder than steel and will easily scratch a glass plate.
Field identification & locations
Identified in the field by its extreme hardness, granular texture, and lack of reaction to acid. It is commonly found in mountain belts and areas of ancient crustal movement. Look for a sugary texture on fresh breaks.
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