metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 (Mohs scale), Color: light grey to tan with faint reddish bands, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to tan with faint reddish bands, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone under high heat and pressure, causing quartz grains to recrystallize and fuse into a solid rock mass.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone; also used as a source of silica for glassmaking and industrial abrasives.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of mountains and ridges because it resists weather better than surrounding rock types.
Field identification & locations
Identify in the field by its hardness (it can scratch glass) and the way it breaks through quartz grains rather than around them. Commonly found in folded mountain ranges.
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