metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 (Mohs), Color: Grey to bluish-grey with white mottling, Luster: Vitreous to dull, Crystal Structure: Trigonal (granular texture), Cleavage: None, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs), Color: Grey to bluish-grey with white mottling, Luster: Vitreous to dull, Crystal Structure: Trigonal (granular texture), Cleavage: None, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used in construction as crushed stone for road beds, railway ballast, and as a decorative stone in architecture and landscaping.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, creating prominent ridges or hills. It is often confused with marble, but quartzite will scratch glass and does not fizz with acid.
Field identification & locations
Identify by its extreme hardness and granular, sugary appearance on freshly broken surfaces. Common in mountain belts where tectonic forces have compressed ancient sedimentary basins.
