metamorphic
Quartzite
Recrystallized Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: White to tan/light brown with slight iron staining, Luster: Vitreous to dull, Crystal structure: Trigonal (granular texture), Cleavage: None (conchoidal or irregular fracture), Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White to tan/light brown with slight iron staining, Luster: Vitreous to dull, Crystal structure: Trigonal (granular texture), Cleavage: None (conchoidal or irregular fracture), Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together. These are found in mountain belts worldwide and vary significantly in age from Precambrian to more recent orogenic events.
Uses & applications
Commonly used in road construction, ballast, and building stone. High-purity quartzite is used to produce glass, silicon metal, and ferrosilicon.
Geological facts
Quartzite is so tough that it often survives erosion better than the rocks surrounding it, forming prominent ridges and hilltops. It is one of the hardest and most durable rocks found on the Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary appearance. Unlike sandstone, it will not crumble into individual grains. Commonly found in areas with historic tectonic activity.
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