metamorphic
Quartzite
Quartzite (composed primarily of silica, SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-tan, grayish-white, or brownish due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); 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: Pinkish-tan, grayish-white, or brownish due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); 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, typically during mountain-building events (orogeny). The original quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop surfaces. Crushed quartzite is used in glassmaking and as a source of silica for industrial silicon production.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of mountains and ridges because it resists erosion better than the surrounding rock. It is often mistaken for marble but can be distinguished because it will not react with acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, granular appearance. Commonly found in ancient mountain belts like the Appalachians or the Scottish Highlands.
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