metamorphic
Ferruginous Quartzite (Iron-stained Quartzite)
Quartzite with Iron oxides (FeO(OH) / Fe2O3)
Hardness: 7 (Mohs scale); Color: Brown, reddish-tan, and dark gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Brown, reddish-tan, and dark gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, reddish-tan, and dark gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure Recrystallize the quartz grains into a dense matrix. The dark staining is due to iron-rich fluids infiltrating the rock after formation or during metamorphic events.
Uses & applications
Used primarily as crushed stone for construction, road ballast, and decorative landscaping. High-purity quartzite is used in the manufacture of glass and silicon.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers, forming prominent ridges and peaks in mountain ranges. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its grainy, 'sugary' texture and extreme hardness (cannot be scratched by a knife). Commonly found in ancient mountain belts and tectonic suture zones.
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