metamorphic
Quartzite
Metamorphic rock primarily composed of Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but can be brownish/orange due to iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but can be brownish/orange due to iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard stone. It is found in mountain ranges and eroded metamorphic terrains globally.
Uses & applications
Commonly used as crushed stone in construction (road ballast), dimension stone for floors and countertops, and in industrial manufacturing as a source of silica for glass and silicon metal.
Geological facts
Quartzite is so tough that it often breaks through the constituent sand grains rather than around them, which distinguishes it from sandstone. Some varieties, like 'snow-white' quartzite, are highly prized for landscaping.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass or a steel knife blade) and its sugary, granular surface that does not fizz in acid. It often forms prominent, weather-resistant ridges in hilly regions.
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