metamorphic
Quartzite (Iron-stained)
Quartzite (SiO2 with Fe-oxides)
Hardness: 7 (Mohs scale), Color: tan to reddish-brown due to iron staining, Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to reddish-brown due to iron staining, Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, causing quartz grains to recrystallize and fuse together. The staining is likely from exposure to iron-rich groundwater.
Uses & applications
Used as crushed stone for road construction, railway ballast, and occasionally as a decorative landscape stone or building facade material.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in high-pressure mountain building events, staying behind as rugged ridges. It is one of the most durable rocks on Earth's surface.
Field identification & locations
Identify in the field by its hardness (will easily scratch glass) and its tendency to break through quartz grains rather than around them. Commonly found in riverbeds or ancient mountain ranges.
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