metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale), Color: White to light grey with yellowish tints, Luster: Vitreous/Glassy, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White to light grey with yellowish tints, Luster: Vitreous/Glassy, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure causes the individual quartz grains to recrystallize and fuse into an interlocking network.
Uses & applications
Used in construction as crushed stone for road base, railway ballast, and in the manufacturing of glass and ceramics due to high silica content. Occasionally used as decorative stone.
Geological facts
Quartzite is so tough and resistant that it often forms the ridges and peaks of mountain ranges because it weathers much more slowly than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that does not rub off. Found in metamorphic belts globally.
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