metamorphic
Quartzite
Metamorphosed Quartz Sandstone (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White, light gray, or tan (sometimes pink or red due to iron oxide); Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking granoblastic grains; Cleavage: None; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, light gray, or tan (sometimes pink or red due to iron oxide); Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking granoblastic grains; Cleavage: None; Specific gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism), typically during mountain-building events. This causes the quartz grains to recrystallize and fuse together.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the manufacturing of glass and ceramics due to high silica content.
Geological facts
Quartzite is so tough that it often survives surface weathering better than surrounding rocks, frequently forming the rugged caps of mountain ridges and hills. It is harder than glass and cannot be scratched by a steel knife.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will scratch glass). Unlike marble, it will not fizz when exposed to acid. Commonly found in folded mountain ranges across the globe, such as the Appalachians or the Alps.
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