metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: White to light gray, 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 light gray, 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 sandstone. High pressure and temperature cause the quartz grains to recrystallize and fuse together, creating a dense, hard rock.
Uses & applications
Used extensively in road construction (as crush), railroad ballast, decorative interior stone, and as a source of silica for glass manufacturing and electronics.
Geological facts
Unlike sandstone which breaks around its grains, quartzite is so strongly fused that it breaks right through the quartz grains. It is one of the most durable and weather-resistant rocks on the Earth's surface.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by a steel nail) and its sugary, crystalline appearance on fresh breaks. It is commonly found in mountain ranges or old shields.
