metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. It is found in mountain belts worldwide where tectonic activity has occurred.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone for flooring or counters. Clean quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so hard that it will scratch steel. It is often more resistant to erosion than the surrounding rock, frequently forming the tops of ridges and mountains.
Field identification & locations
Identify in the field by its extreme hardness and the fact that it breaks across the grains, rather than around them like sandstone. Often found in riverbeds or as glacial erratic cobbles.
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