metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown to tan (due to iron oxide staining); Luster: Vitreous to dull/sandy; Crystal structure: Non-foliated, granular; Fracture: Conchoidal to irregular; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown to tan (due to iron oxide staining)
- Luster
- Vitreous to dull/sandy
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown to tan (due to iron oxide staining); Luster: Vitreous to dull/sandy; Crystal structure: Non-foliated, granular; Fracture: Conchoidal to irregular; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. This specimen appears to be water-worn, likely from a river or beach environment.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone decorative flooring. High-purity quartzite is also a source of silica for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often survives intense weathering and erosion better than the rocks surrounding it, leading to the formation of ridges or caps on mountains. It is harder than steel and will easily scratch a glass plate.
Field identification & locations
Identify in the field by its grainy, sandpaper-like surface that nonetheless breaks through the quartz grains rather than around them. Commonly found in folded mountain belts. Collectors look for smooth, river-tumbled pieces for polishing.
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