metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale), Color: White to grayish with tan iron staining, Luster: Vitreous to dull, Crystal structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White to grayish with tan iron staining, Luster: Vitreous to dull, Crystal structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop surfaces. Crushed quartzite is used as a source of silica in glass manufacturing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of ridges and mountains because it resists weathering better than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and the way it breaks through sand grains rather than around them. Commonly found in folded mountain belts.
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