metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or yellowish (due to iron oxide staining); Luster: Vitreous to dull; Crystal structure: Trigonal; Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or yellowish (due to iron oxide staining)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or yellowish (due to iron oxide staining); Luster: Vitreous to dull; Crystal structure: Trigonal; Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize and fuse into a solid mass.
Uses & applications
Used in construction as road ballast, railway track bedding, and building stone. Fine specimens are used for landscaping and occasionally as semiprecious stones in jewelry.
Geological facts
Quartzite is so hard and tough that it often outlasts the surrounding rock in the field, frequently forming the tops of ridges and mountains. It can break through quartz grains rather than around them like sandstone.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and grainy but crystalline texture. Found globally in mountainous regions or as rounded river cobbles.
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