metamorphic
Quartzite
Metamorphosed quartz sandstone (SiO2)
Hardness of 7 on the Mohs scale, colors range from white and gray to pink and yellow, vitreous to greasy luster, trigonal crystal system within a massive or granular structure, conchoidal fracture with no true cleavage, specific gravity around 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, colors range from white and gray to pink and yellow, vitreous to greasy luster, trigonal crystal system within a massive or granular structure, conchoidal fracture with no true cleavage, specific gravity around 2.65.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, typically through tectonic compression during mountain-building events (orogeny).
Uses & applications
Used in construction, as crushed stone for road bases, in manufacturing refractory bricks, as decorative dimension stone, and occasionally in lapidary arts.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why ridges formed of quartzite often survive as prominent hills or mountains while surrounding softer rocks erode away.
Field identification & locations
Can be identified in the field by its sugary texture on broken surfaces, extreme hardness that easily scratches glass and resists steel, and the fact that it breaks across the quartz grains rather than around them like sandstone.
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