metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often yellow or brown due to iron oxides; Luster: Vitreous to dull; Structure: Granular, interlocking quartz crystals; Cleavage: None (conchoidal fracture); 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: typically white to gray, often yellow or brown due to iron oxides; Luster: Vitreous to dull; Structure: Granular, interlocking quartz crystals; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together. These rocks can date from the Precambrian to recent eras.
Uses & applications
Used in construction as crushed stone for road grit and railroad ballast, as decorative building stone, in the production of glass and ceramics, and as a raw material for silicon-based products.
Geological facts
Quartzite is so tough that it often survives erosion better than any other rock type, frequently forming the tops of mountain ranges and ridges. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it cannot be scratched by a steel blade). Unlike marble, it will not fizz when exposed to hydrochloric acid. Commonly found in folded mountain belts globally.
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