metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: Smoky grey, reddish-brown to white, Luster: Vitreous to waxy, Crystal structure: Trigonal (microcrystalline), Cleavage: None, specific gravity: 2.63-2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Smoky grey, reddish-brown to white, Luster: Vitreous to waxy, Crystal structure: Trigonal (microcrystalline), Cleavage: None, specific gravity: 2.63-2.65
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together into a dense, crystalline rock.
Uses & applications
Used extensively in construction as crushed stone for road beds, railway ballast, and as a decorative building stone. High-purity quartzite is used to produce glass and metallic silicon.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and hills. Unlike sandstone, when quartzite breaks, it fractures across the quartz grains rather than around them.
Field identification & locations
Identify in the field by its hardness (will scratch glass easily) and its sugary, crystalline appearance on fresh surfaces. It is commonly found in mountainous regions or ancient cratons worldwide.
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