metamorphic
Iron-Stained Quartzite
Quartzite (chemically SiO2 with Fe2O3/FeO(OH) staining)
Hardness: 7 (Mohs scale), Color: Rusty brown, orange, and tan due to oxidation, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture).
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Physical properties
Hardness: 7 (Mohs scale), Color: Rusty brown, orange, and tan due to oxidation, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture).
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism), causing quartz grains to recrystallize. The orange-brown color comes from the secondary infiltration of iron oxides like limonite or hematite.
Uses & applications
Used in construction as crushed stone, road ballast, and decorative landscaping rock. Exceptionally durable for architectural facing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it weathers much slower than surrounding rocks.
Field identification & locations
Identified by its ability to scratch glass easily and its sugary, granular texture. Unlike sandstone, quartzite breaks through the quartz grains rather than around them. Found globally in ancient mountain belts.
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