metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: light grey to white with translucent patches, Luster: vitreous to waxy, Crystal structure: Trigonal (microcrystalline), Cleavage: none (conchoidal fracture), SG: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to white with translucent patches, Luster: vitreous to waxy, Crystal structure: Trigonal (microcrystalline), Cleavage: none (conchoidal fracture), SG: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone subjected to extreme heat and pressure, causing quartz grains to recrystallize and fuse.
Uses & applications
Used as crushed stone for road construction, railway ballast, decorative stone in architecture, and as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges and hilltops. It will scratch glass easily unlike many similar-looking rocks.
Field identification & locations
Identify by its extreme hardness and the fact that it breaks through quartz grains rather than around them. Found globally in ancient mountain belts.
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