metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: White, gray, or tan (often with pinkish/reddish iron staining), Luster: Vitreous to dull, Crystal structure: Trigonal (granular texture), 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 (often with pinkish/reddish iron staining), Luster: Vitreous to dull, Crystal structure: Trigonal (granular texture), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, eliminating pore space. Found in orogenic belts worldwide.
Uses & applications
Used extensively in road construction as crushed stone, as railway ballast, and in building stone/flooring. High-purity quartzite is used to produce glass, silicon metal, and ferrosilicon for the electronics industry.
Geological facts
Unlike sandstone, which breaks around the sand grains, quartzite is so hard and densely fused that it breaks right through the grains. It is extremely resistant to chemical weathering and often forms the peaks of rugged mountain ranges.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and a granular, sugary texture. It is often found in mountainous areas where old sedimentary basins have been uplifted and compressed.
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