metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, sometimes yellowish/brownish; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (breaks with conchoidal fracture through grains); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, sometimes yellowish/brownish
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, sometimes yellowish/brownish; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (breaks with conchoidal fracture through grains); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure. This causes the original quartz grains to recrystallize into an interlocking mosaic of quartz crystals.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone for flooring or wall coverings. Crushed quartzite is also used as a source of silica for glass making and metallurgy.
Geological facts
Quartzite is so hard that it will scratch glass and steel. Unlike sandstone, which breaks around its grains, quartzite breaks across the grains because the metamorphic process makes the bond between grains stronger than the grains themselves.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, granular surface that does not rub off like sand. It is commonly found in mountain ranges and areas with exposed Precambrian or Paleozoic metamorphic rocks.
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