metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellow/brown due to iron staining; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none, breaks with conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or yellow/brown due to iron staining
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellow/brown due to iron staining; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none, breaks with conchoidal fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse into a solid network of quartz crystals. Most quartzite is from the Proterozoic or Paleozoic eras.
Uses & applications
Used as crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics. Polished varieties are used for countertops and floor tiles.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges of mountain ranges because it resists erosion much better than surrounding rocks. It was also used by prehistoric humans to create stone tools when flint was unavailable.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass and steel) and its grainy, granular look that resembles sandstone but cannot be rubbed off into individual sand grains. It is extremely common in metamorphic belts and mountain ranges worldwide.
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