metamorphic
Quartzite
Metamorphosed Quartz Sandstone (primarily SiO2)
Hardness: 7 (Mohs scale), Color: White, gray, or light tan, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White, gray, or light tan, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Specific Gravity: 2.6-2.7
Formation & geological history
Quartzite forms when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used as decorative stone in landscaping, crushed stone for road construction and railway ballast, and occasionally for high-quality countertops or architectural cladding.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the crests of ridges and mountains because it resists erosion much better than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (it easily scratches glass) and its sugary, granular texture; unlike sandstone, it breaks through the grains rather than around them.
