metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, yellowish-brown, or reddish due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None, breaks with a conchoidal or splintery fracture; Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, yellowish-brown, or reddish due to iron oxide staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, yellowish-brown, or reddish due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None, breaks with a conchoidal or splintery fracture; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together into a dense, hard mass. Much Quartzite dates back to the Proterozoic or Paleozoic eras.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used as a source of silica for glassmaking and silicon production.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the resistant caps of ridges and mountains. Unlike sandstone which breaks around grains, quartzite breaks through the grains.
Field identification & locations
Identify in the field by its extreme hardness (scratches glass) and its sugary, granular appearance. Commonly found in mountainous regions or as river-worn cobbles. It will not fizz with acid, distinguishing it from marble.
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