metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellow/brown due to iron impurities; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellow/brown due to iron impurities; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, eliminating pore space. Often found in Precambrian or Paleozoic formations.
Uses & applications
Used as a decorative stone in landscaping, a durable construction aggregate for roads and railway ballast, and in the manufacturing of glass and ceramics due to its high silica content.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, frequently forming the caps of hills or ridges. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its sugary, granular texture and its inability to be scratched by a steel knife. It will break across the original sand grains rather than around them, unlike sandstone. Common in mountainous regions like the Appalachians or the Alps.
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