metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Cream, tan, or yellowish-brown due to iron impurities; Luster: Waxy to vitreous; Structure: Crystalline mosaic of interlocking quartz grains; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Cream, tan, or yellowish-brown due to iron impurities
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Cream, tan, or yellowish-brown due to iron impurities; Luster: Waxy to vitreous; Structure: Crystalline mosaic of interlocking quartz grains; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under extreme heat and pressure, typically during mountain-building events. The original sand grains recrystallize and fuse together.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and building stone. Highly durable and weather-resistant, making it ideal for outdoor landscaping and high-end countertops.
Geological facts
Quartzite is so hard that it can scratch glass and steel. It is often tougher than its parent rock, sandstone, because the boundaries between the original grains disappear during metamorphism.
Field identification & locations
Identify in the field by its extreme hardness and the fact that it breaks across the grains rather than around them (unlike sandstone). It is commonly found in ancient mountain belts and riverbeds as rounded cobbles.
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