metamorphic
Quartzite
Metamorphosed Sandstone (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or reddish-brown due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None, breaks with conchoidal or uneven fracture.
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or reddish-brown due to iron oxide staining
- Luster
- Vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or reddish-brown due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None, breaks with conchoidal or uneven fracture.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, hard mass.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as a raw material for producing glass and silicon metal. Polished varieties are used for countertops and flooring.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in weathering processes, frequently forming the peaks of ridges and mountains. It is harder and more durable than granite.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that doesn't rub off. It is commonly found in mountainous regions or ancient shield areas like the Appalacians or the Canadian Shield.
