metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: Pinkish-red due to iron oxide inclusions, Luster: Vitreous to dull, Crystal structure: Trigonal (granular), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7.
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Physical properties
Hardness: 7 (Mohs scale), Color: Pinkish-red due to iron oxide inclusions, Luster: Vitreous to dull, Crystal structure: Trigonal (granular), 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 during regional metamorphism, causing quartz grains to recrystallize and fuse together. Often Precambrian to Paleozoic in age.
Uses & applications
Used in construction as crushed stone, railway ballast, decorative landscaping, and occasionally as a flux in metallurgy. High purity quartzite is used to produce glass and silica products.
Geological facts
Quartzite is so hard that it will break across the original quartz grains rather than around them, which distinguishes it from sandstone. This specific rounded specimen is a river-worn or glacial cobble.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and granular, sugary appearance. Found globally in mountainous regions or as rounded pebbles in glacial drift and riverbeds.
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