metamorphic
Quartz / Quartzite
Quartzite (primarily Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale), Color: White to light tan, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: White to light tan, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under high heat and pressure, the sand grains recrystallize and fuse together into a dense, hard rock. Found in mountain belts globally.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as a raw material for glass and ceramics. Pure forms are used in the production of silicon and silicon carbide.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming prominent ridges and peaks. It is frequently mistaken for marble, but can be distinguished because it will not fizz in acid and is much harder.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and its grainy, sandpaper-like texture that doesn't rub off. Commonly found in areas with ancient folded mountain ranges.
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