metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: Pinkish-red to brownish-purple, Luster: Vitreous to dull, Crystal Structure: Non-foliated granoblastic, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Pinkish-red to brownish-purple, Luster: Vitreous to dull, Crystal Structure: Non-foliated granoblastic, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. The quartz grains recrystallize into a locked mosaic. Commonly found in Precambrian orogenic belts and folded mountain ranges.
Uses & applications
Used as railway ballast, crushed stone for road construction, decorative flooring, wall coverings, and countertops. Ground quartzite is used in glass making and ceramics.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of hills and ridges because it resists weather better than the surrounding rock. It is often harder than the steel of a pocket knife.
Field identification & locations
Identify by its inability to be scratched by steel and its grainy, sandpaper-like texture that does not rub off. Commonly found in South Dakota (Sioux Quartzite), the Appalachians, and the Alps.
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