metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: White, gray, or tan with possible light green/yellow tinting, Luster: Vitreous to dull, Crystal Structure: Hexagonal (trigonal) in grains, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White, gray, or tan with possible light green/yellow tinting, Luster: Vitreous to dull, Crystal Structure: Hexagonal (trigonal) in grains, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. It undergoes extreme heat and pressure which causes the individual quartz grains to recrystallize and fuse together. Often found in orogenic belts (mountain-building regions).
Uses & applications
Used in construction, road ballast, as a source for silica in glassmaking, and sometimes as dimension stone or decorative landscaping pebbles.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges it was formed in, becoming the 'capstone' on ridge tops. Unlike sandstone, quartzite breaks across its grains rather than around them because the grains are so tightly fused.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary appearance. Found globally in ancient shield areas. Low value for common specimens but high utility in industry.
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