metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, fractures conchoidally; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, fractures conchoidally; Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the original quartz grains to recrystallize and fuse into a solid rock. This typically occurs during regional metamorphism at convergent plate boundaries.
Uses & applications
Used in construction for road ballast and roofing granules, as a decorative stone in architecture and landscaping, in the manufacturing of glass and ceramics, and for high-quality gravel.
Geological facts
Quartzite is extremely durable and weather-resistant; it is so hard that it will scratch glass and steel. Most quartzite is over 90% quartz, making it one of the most silica-rich rocks on Earth.
Field identification & locations
Identify in the field by its grainy texture that looks like sandstone but breaks across the grains rather than around them due to the fusing process. It is commonly found in mountain ranges such as the Appalachians or the Alps.
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