metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with reddish/brown staining from iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, 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, often with reddish/brown staining from iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, conchoidal fracture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under high heat and pressure, typically during mountain-building events (orogeny). The quartz grains recrystallize and fuse together.
Uses & applications
Used in construction for road ballast, roofing granules, and as a decorative stone. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the peaks of ridges and mountains. It is harder than steel and will easily scratch a knife blade.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, crystalline texture that breaks across grain boundaries rather than around them. Commonly found in metamorphic belts worldwide.
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