metamorphic
Quartzite
Quartzite
Hardness: 7 on Mohs scale. Color: White, gray, or yellowish-brown due to iron impurities. Luster: Vitreous to greasy. Crystal structure: Granular, interlocking quartz crystals. Cleavage: None (breaks with a conchoidal or irregular fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White, gray, or yellowish-brown due to iron impurities
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale. Color: White, gray, or yellowish-brown due to iron impurities. Luster: Vitreous to greasy. Crystal structure: Granular, interlocking quartz crystals. Cleavage: None (breaks with a conchoidal or irregular fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartzaceous sandstone. Under intense heat and pressure, the original quartz grains recrystallize and fuse together into a dense, interlocking network. Geological age spans from Precambrian to Cenozoic.
Uses & applications
Used widely in construction as crushed stone for road base, railway ballast, and concrete aggregate. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal. Also used as decorative stone in architecture.
Geological facts
Quartzite is so tough that it often resists weathering better than surrounding rocks, creating prominent ridges and hills known as quartzite monadnocks. It can be distinguished from sandstone because it fractures through the grains, rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and granular crystalline appearance that sparkles slightly in light. Found in metamorphic mountain belts globally, such as the Appalachian Mountains in the USA and parts of the Alps.
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