metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with a reddish-brown iron inclusion; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.63-2.65
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with a reddish-brown iron inclusion
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with a reddish-brown iron inclusion; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.63-2.65
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, eliminating the pore spaces found in its original sedimentary state.
Uses & applications
Used in construction as road ballast, gravel, and flooring. Highly pure varieties are used to produce silica sand for glassmaking and metallurgical applications. Also used as a decorative stone.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along their boundaries, unlike sandstone. It is often more resistant to weathering than the surrounding rock, often forming the crests of ridges and mountains.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its crystalline, sugary appearance. It will not effervesce with acid, distinguishing it from marble. Found globally in ancient mountain belts.
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