metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: White to grey/light tan, Luster: Vitreous to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White to grey/light tan, Luster: Vitreous to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), 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, solid rock.
Uses & applications
Used as a decorative stone in construction, countertops, floor tiles, and as a raw material for glass making and silica sand production.
Geological facts
Quartzite is so hard that it can scratch glass and steel. It is often confused with marble, but while marble will react with acid, quartzite will not.
Field identification & locations
Identify in the field by its extreme hardness and the way it breaks through quartz grains rather than around them (unlike sandstone). Found globally in folded mountain belts.
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