metamorphic
Quartzite (Ferruginous)
Metamorphosed Sandstone (SiO2 with Fe2O3 inclusions)
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, or gray; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown, tan, or gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, or gray; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together. The reddish tint suggests the presence of iron oxide (hematite) during formation.
Uses & applications
Used extensively in construction as road ballast, railway track ballast, and as a decorative stone in landscaping or floor tiles. Also used as a source of silica in glass manufacturing.
Geological facts
Quartzite is so tough that it often survives intense weathering better than the surrounding rocks, frequently forming the caps of hills and ridges. It is often harder than the steel of a knife blade.
Field identification & locations
Identify by its hardness (it will scratch glass) and its sugary, granular texture. Unlike sandstone, quartzite breaks across the quartz grains rather than around them. Found globally in mountainous regions.
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