metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: Tan, brown, or grayish. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, exhibits conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or grayish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, brown, or grayish. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, exhibits conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, forming an interlocking crystalline structure. Typically Precambrian to Paleozoic in age.
Uses & applications
Used widely as crushed stone for road construction and railway ballast. High-purity quartzite is used in the manufacture of glass, silicon, and ceramics. Also used as decorative stone in landscaping and interior design.
Geological facts
Quartzite is so tough that it often survives erosion better than other rocks, frequently capping hills and mountain ridges. When broken, quartzite will fracture through the grains rather than around them, unlike its parent rock, sandstone.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Look for a sugary texture on fresh surfaces. Common in mountain belts where tectonic plates have collided.
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