metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Yellowish-tan/buff; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None, conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-tan/buff
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-tan/buff; 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 regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. Most deposits are Proterozoic to Paleozoic in age.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the manufacturing of glass and ceramics due to its high silica content.
Geological facts
Quartzite is so hard that it can easily scratch glass and steel. It is more resistant to weathering than the sandstone it originated from, often forming the caps of ridges and mountains.
Field identification & locations
Identify in the field by its extreme hardness and the fact that fractures go through the industrial quartz grains rather than around them (unlike sandstone). Found globally in folded mountain belts like the Appalachians.
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