metamorphic
Quartzite
SiO2 (Metamorphosed Sandstone)
Hardness: 7 (Mohs scale), Color: tan, white, or light gray, Luster: vitreous to dull, Crystal structure: trigonal (hexagonal system), Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7.
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, white, or light gray, Luster: vitreous to dull, Crystal structure: trigonal (hexagonal system), Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the original quartz grains to recrystallize and fuse together. Typically Precambrian to Cenozoic.
Uses & applications
Used as building stone, decorative landscaping, industrial silica supply for glass making, and as a durable material for road ballast.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the crests of ridges and peaks because it resists weathering better than the surrounding rock.
Field identification & locations
Identify by its extreme hardness (scratches glass) and grainy, crystalline texture. It is commonly found in mountainous regions or ancient shield areas. Collectors look for high purity or unique iron staining.
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