metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, or grey; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Granular texture.
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown, tan, or grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, or grey; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Granular texture.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the sand grains to recrystallize and fuse together.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop surfaces; also used as a decorative stone in landscaping.
Geological facts
Quartzite is so tough that it often survives intense weathering better than the rocks around it, creating prominent ridges or hills. It will scratch glass easily.
Field identification & locations
Identify by its extreme hardness and its characteristic of breaking through the quartz grains rather than around them (unlike sandstone). Commonly found in folded mountain belts.
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