metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be tan or yellow due to impurities; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- 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 tan or yellow due to impurities; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. The geological age varies depending on the deposit, ranging from Precambrian to more recent tectonic periods.
Uses & applications
Used widely in construction as crushed stone for road bases, railway ballast, and decorative building stone. High-purity quartzite is used to produce glass, silicon metal, and abrasive tools.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming ridges or hills known as 'quartzite monadnocks.' It is much harder than the sandstone from which it originates and will scratch glass easily.
Field identification & locations
Identified by its sugary texture and extreme hardness (it cannot be scratched by a steel knife). Unlike sandstone, which breaks around grains, quartzite breaks through the grains. It is commonly found in mountainous regions or riverbeds as smoothed pebbles.
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