metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale), Color: tan, yellow, gray, or rust-colored due to impurities; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Grainy, sand-paper like texture but very hard.
- Color
- tan, yellow, gray, or rust-colored due to impurities
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, yellow, gray, or rust-colored due to impurities; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Grainy, sand-paper like texture but very hard.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism), causing quartz grains to recrystallize and fuse together into a dense rock.
Uses & applications
Used as a decorative stone in landscaping, a source of silica for glassmaking, and in crushed form for road ballast and construction aggregate.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it erodes much slower than the surrounding rock.
Field identification & locations
Identify in the field by its inability to be scratched by steel and its tendency to break through the sand grains rather than around them. Common in folded mountain belts.
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