metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: tan, reddish-brown (likely due to iron oxide staining), grayish-white; Luster: dull to vitreous; Crystal structure: Trigonal (granular texture); Cleavage: none; Specific gravity: approx. 2.64-2.65.
- Hardness
- 7 on Mohs scale
- Luster
- dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, reddish-brown (likely due to iron oxide staining), grayish-white; Luster: dull to vitreous; Crystal structure: Trigonal (granular texture); Cleavage: none; Specific gravity: approx. 2.64-2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under high heat and pressure, causing the original quartz grains to recrystallize and fuse together. Often associated with Proterozoic or Paleozoic eras.
Uses & applications
Used in construction for road ballast, floor tiles, and decorative stone. Historically used to make stone tools. It is also a source of silica for glass and silicon production.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it resists weathering better than the surrounding rock types. It is harder than steel and will scratch a glass plate easily.
Field identification & locations
Identify in the field by its extreme hardness and granular, sugary appearance on a fresh break. Unlike sandstone, it will not crumble easily, and unlike limestone, it will not fizz with acid. Common in ancient mountain belts.
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