metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: Brownish-tan due to iron oxide impurities, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal to irregular fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-tan due to iron oxide impurities, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal to irregular fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together into a dense, hard rock. Can be found in mountain belts and Precambrian shields worldwide.
Uses & applications
Historically used for making stone tools due to its hardness and fracture patterns. Modern uses include construction aggregates, road ballast, decorative building stone, and dimension stone for countertops or tiles.
Geological facts
Quartzite is so strong that when broken, it fractures through the quartz grains rather than along the boundaries between them, unlike its parent stone, sandstone. It is one of the most durable rocks on Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and sugary, granular appearance on fresh surfaces. Often found in hilly or mountainous terrain as it is highly resistant to erosion.
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