metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs), Color: Gray, white, or tan (can be pinkish), Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline/interlocking), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs), Color: Gray, white, or tan (can be pinkish), Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline/interlocking), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The original quartz sand grains recrystallize and fuse together.
Uses & applications
Used in construction as crushed stone or decorative building stone, in glass manufacturing if high purity, and as a component in metallurgy.
Geological facts
Quartzite is so tough that it often survives intense weathering better than surrounding rocks, frequently forming the caps of ridges and mountain peaks.
Field identification & locations
Identify by its hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that lacks the visible pore spaces of sandstone. Found globally in ancient mountain belts and shield areas.
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