metamorphic
Quartzite
Quartzite (chiefly SiO2)
Hardness: 7 (Mohs scale), Color: light grey to purple/brown, Luster: vitreous to dull, Structure: Granular/non-foliated, Cleavage: None/Conchoidal fracture
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to purple/brown, Luster: vitreous to dull, Structure: Granular/non-foliated, Cleavage: None/Conchoidal fracture
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone subjected to high heat and pressure, causing the original quartz grains to recrystallize and fuse into a solid rock.
Uses & applications
Used as a decorative stone in construction, road ballast, railroad tracks, and historically for stone tools due to its extreme hardness and durability.
Geological facts
Quartzite is so hard that when it breaks, it fractures through the quartz grains themselves rather than around them as sandstone does. It is one of the most durable rocks on the Earth's surface.
Field identification & locations
Identify in the field by its inability to be scratched by steel and its granular, sugary texture. Common in ancient mountain belts and shield areas.
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