metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: white to light tan; Luster: vitreous to matte; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- white to light tan
- Luster
- vitreous to matte
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Physical properties
Hardness: 7 on Mohs scale; Color: white to light tan; Luster: vitreous to matte; 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 under intense heat and pressure, typically during regional mountain-building events. The original sand grains recrystallize into a dense, interlocking mosaic of quartz.
Uses & applications
Used extensively in construction as road ballast, railroad track bedding, and as a decorative stone for indoor/outdoor landscaping. High-purity quartzite is used in the manufacture of glass and silicon.
Geological facts
Quartzite is so tough that it often survives the weathering process longer than surrounding rocks, frequently forming the tops of ridges and hills. It is often confused with marble but will easily scratch glass.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and its sugary, crystalline texture. It is commonly found in ancient mountain belts and as rounded river or beach cobbles.
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