metamorphic
Quartzite with Iron Staining
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale; color is off-white to light gray with distinctive brownish-yellow iron oxide banding; vitreous to greasy luster; massive crystal structure; no cleavage; specific gravity of 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; color is off-white to light gray with distinctive brownish-yellow iron oxide banding; vitreous to greasy luster; massive crystal structure; no cleavage; specific gravity of 2.65.
Formation & geological history
Formed when quartz-rich sandstone or chert is subjected to high heat and pressure, typically through tectonic metamorphism. The original quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used in construction, as crushed stone for road bases, in railroad ballast, and occasionally as decorative stone or in landscaping.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why quartz-rich rocks often survive long transport in rivers to become smooth pebbles.
Field identification & locations
Can be identified in the field by its extreme hardness (scratches glass easily), lack of effervescence with acid, and sugary textured fracture surfaces if broken. Found globally in mountainous regions and ancient river beds.
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