metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, tan, or brown; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, tan, or brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, tan, or brown; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events (orogenic processes). The grains of quartz recrystallize into a dense, interlocking mosaic.
Uses & applications
Used in construction as crushed stone for road grit and railway ballast, as dimension stone for counter tops and flooring, and occasionally in glass manufacturing if the silica content is extremely high.
Geological facts
Quartzite is so durable that it often forms the crests of ridges and mountains because it resists weathering better than the surrounding rock. It is often mistaken for marble, but can be distinguished by its superior hardness.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and lack of reaction to acid. It has a sugary or grainy appearance but breaks across the grains rather than around them. Found globally in ancient mountain belts.
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