metamorphic
Quartzite
Quartzite (SiO2 with impurities)
Hardness: 7 on Mohs scale; Color: Reddish-brown, maroon, or pink; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown, maroon, or pink
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown, maroon, or pink; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse into a dense, interlocking matrix. This often occurs during mountain-building events.
Uses & applications
Used as decorative stone in architecture, railway ballast, road aggregate, and as a raw material for glass and ceramics due to high silica content. Occasionally used in jewelry or as a garden stone.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of ridges and hills. When broken, quartzite breaks across the individual sand grains, whereas sandstone breaks around them.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary texture. Common in Appalachian Mountains and parts of the upper Midwest US.
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