metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: tan to light brown, Luster: vitreous or sugary, Crystal structure: Trigonal (granular texture), Specific Gravity: 2.6-2.7. It is very durable and lacks cleavage.
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to light brown, Luster: vitreous or sugary, Crystal structure: Trigonal (granular texture), Specific Gravity: 2.6-2.7. It is very durable and lacks cleavage.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (regional metamorphism), causing the quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used extensively in construction as road ballast, gravel, and dimension stone for flooring or wall coverings. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so hard that when it breaks, the fracture cuts through the individual quartz grains rather than around them, distinguishing it from sandstone. It is often resistant to weathering and forms prominent ridges.
Field identification & locations
Identify by its hardness (it will easily scratch glass) and its sugary, crystalline texture. It is ubiquitous in metamorphic belts worldwide, such as the Appalachian Mountains or the Alps.
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