metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-brown or tan; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-brown or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-brown or tan; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz sandstone. The high heat and pressure cause the individual quartz grains to recrystallize and fuse together with silica. This specimen appears water-worn, likely from a fluvial (river) environment.
Uses & applications
Used in construction for road ballast, flooring, and wall coverings. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal. It is also used in landscaping and as a lapidary material.
Geological facts
Quartzite is so tough that it often breaks through the quartz grains rather than along the boundaries between them, unlike sandstone. It is highly resistant to chemical weathering and often forms the ridges of mountain ranges.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its grainy, sugary appearance despite being a solid rock. Common in geologically old mountain belts and river beds draining those areas.
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