metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None/conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, or grayish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; 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 mountain-building events (orogeny).
Uses & applications
Used extensively in construction as road ballast, gravel, and dimension stone. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, creating prominent ridges and hills. It is resistant to chemical weathering.
Field identification & locations
Identify by its hardness (cannot be scratched by a steel knife) and the fact that it breaks through the quartz grains rather than around them (unlike sandstone). Commonly found in folded mountain belts globally.
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