metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, breaks with a conchoidal or splintery fracture.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, breaks with a conchoidal or splintery fracture.
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, causing quartz grains to recrystallize and fuse together. Typically Precambrian to Paleozoic in age.
Uses & applications
Used in construction as crushed stone for road ballast, as a dimension stone for floor tiles and countertops, and in manufacturing for silica production.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges and hilltops. It is one of the hardest and most chemically resistant rocks on the Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It is commonly found in mountain belts and shield areas globally.
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