metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: tan, yellow, or reddish-brown due to iron impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- tan, yellow, or reddish-brown due to iron impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, yellow, or reddish-brown due to iron impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. Under intense heat and pressure, the sand grains recrystallize and fuse together into a dense, hard rock. Can range from Proterozoic to more recent geological ages.
Uses & applications
Used as crushed stone for road construction and railway ballast. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal. It is also used as a decorative building stone and for countertops.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the peaks of mountain ranges because it resists weathering better than surrounding rocks. It can be distinguished from sandstone because it breaks across the grains rather than around them.
Field identification & locations
Identify in the field by its hardness (it should easily scratch glass) and its sugary, crystalline appearance on fresh surfaces. Often found in glaciated areas as rounded cobbles or in metamorphic mountain belts.
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