metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale), Color: White, gray, or yellowish-tan, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White, gray, or yellowish-tan, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. These rocks can date back to any geological era, frequently found in Precambrian shields.
Uses & applications
Used in construction as crushed stone for road beds, railway ballast, and decorative building stone. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often breaks through the quartz grains rather than along their boundaries. It is one of the most chemically and physically resistant rocks found on Earth's surface.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture. Commonly found in mountain ranges or as water-worn cobbles in riverbeds. Often confused with marble, but quartzite will not react with acid.
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