metamorphic
Quartzite (Ferruginous)
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: White to tan with reddish-brown iron staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to tan with reddish-brown iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to tan with reddish-brown iron staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, typically during mountain-building events (orogeny). The reddish hue comes from iron oxide infiltration (hematite or limonite) during or after metamorphism.
Uses & applications
Used as a decorative stone, crushed stone for road construction, railway ballast, and occasionally in glass manufacturing if high purity. Collectors value specimens with unique iron patterns.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is much more resistant to weathering than the sandstone it originated from, often forming the caps of ridges and mountains.
Field identification & locations
Identify by its inability to be scratched by a steel knife and its sugary texture where individual sand grains have fused. Commonly found in metamorphic belts like the Appalachians or the Rocky Mountains.
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