metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or light tan; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or light tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or light tan; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events. The individual quartz grains recrystallize into a locked mosaic.
Uses & applications
Used as decorative stone in construction, road ballast, railway tracks, and sometimes as a source of silica for industrial manufacturing.
Geological facts
Quartzite is so tough that it often survives intense weathering better than surrounding rocks, frequently forming the tops of ridges and hills. It can be distinguished from sandstone because it breaks through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of foliation. Commonly found in folded mountain belts globally. It feels much smoother and denser than common sandstone.
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