metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be brownish-red due to iron inclusions; Luster: Vitreous to dull; Crystal structure: Trigonal (hexagonal); Cleavage: None, exhibits conchoidal fracture.
- 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, but can be brownish-red due to iron inclusions; Luster: Vitreous to dull; Crystal structure: Trigonal (hexagonal); Cleavage: None, exhibits conchoidal fracture.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under high heat and pressure, the sand grains recrystallize and fuse together into a dense, crystalline mass. It can be found in mountain ranges of various geological ages from Precambrian to Mesozoic.
Uses & applications
Used primarily as decorative stone, crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics due to its high silica content.
Geological facts
Quartzite is so hard that it will scratch glass and steel. In prehistoric times, it was occasionally used as a substitute for flint to create stone tools, though it is more difficult to work with due to its granular internal structure.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, granular texture which sparkles under light. It is commonly found in the Appalachian Mountains, Lake Superior region, and the Alps. Unlike limestone, it will not fizz with acid.
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