metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or brownish; Luster: Vitreous to dull; Crystal structure: Hexagonal (as individual quartz grains); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or brownish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or brownish; Luster: Vitreous to dull; Crystal structure: Hexagonal (as individual quartz grains); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together. These specimens can range from Precambrian to Cenozoic in age.
Uses & applications
Used heavily in construction for road ballast, roofing granules, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers, forming prominent ridges and hilltops. It is frequently more durable than granite. Historical artifacts like Neolithic scrapers were sometimes fashioned from it.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture. Unlike sandstone, quartzite breaks across the grains rather than around them. Found globally in mountainous regions and glacial till.
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