metamorphic
Quartzite (Ferruginous)
Metamorphosed Quartz Sandstone (SiO2 with Fe2O3 inclusions)
Hardness: 7 on Mohs scale; Color: Pinkish-red to tan due to iron oxides; Luster: Dull to vitreous; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture)
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-red to tan due to iron oxides
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-red to tan due to iron oxides; Luster: Dull to vitreous; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing recrystallization. This specific specimen appears to be a water-worn river cobble, likely of Proterozoic or Paleozoic age.
Uses & applications
Used in construction as road ballast, decorative landscaping, and occasionally as a semi-precious stone for lapidary work (cabochons) when highly colored.
Geological facts
Quartzite is so tough that it often breaks through the individual quartz grains rather than along their boundaries. It is more resistant to weathering than the original sandstone.
Field identification & locations
Identify in the field by its hardness (it will scratch glass easily) and its sugary, granular texture. Commonly found in riverbeds and glacial tills where harder rocks survive transport.
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