metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: tan to yellowish-white, Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline grains), Cleavage: Indistinct/Conchoidal fracture
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to yellowish-white, Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline grains), Cleavage: Indistinct/Conchoidal fracture
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used in construction as a decorative stone, road ballast, roofing granules, and as a source of high-purity silica for glass and abrasive manufacturing.
Geological facts
Quartzite is so hard and durable that it often forms the resistant caps of ridges and mountains because it resists erosion more effectively than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness; it will easily scratch glass. Unlike sandstone, when broken, quartzite breaks through the quartz grains rather than around them.
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