metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: light grey to white with slight tan staining, Luster: vitreous to grainy, Crystal structure: trigonal (microcrystalline), Cleavage: none, Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to white with slight tan staining, Luster: vitreous to grainy, Crystal structure: trigonal (microcrystalline), Cleavage: none, Specific gravity: 2.6-2.7
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, creating a very dense and durable rock.
Uses & applications
Used in construction as road ballast, gravel, roofing granules, and as a decorative stone. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so tough that it often survives intense erosion better than the rocks around it, resulting in prominent ridges and hills. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it cannot be scratched by a steel nail). Breaking it reveals a fracture that goes through the quartz grains rather than around them, unlike sandstone. It is found in mountain ranges globally.
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