metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or brown staining from iron oxides; Luster: vitreous to waxy; Crystal structure: trigonal (granular texture); Cleavage: none; Specific gravity: 2.6 to 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 to gray, often with yellow or brown staining from iron oxides; Luster: vitreous to waxy; Crystal structure: trigonal (granular texture); Cleavage: none; Specific gravity: 2.6 to 2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse into a solid, tight network of crystals. Most specimens dates back to the Proterozoic or Paleozoic eras.
Uses & applications
Used in construction as crushed stone for road ballast, as a decorative stone in architecture (slabs for countertops), and occasionally in the manufacture of glass and ceramics if high purity is present.
Geological facts
Quartzite is so tough that it often outlasts surrounding rocks; many hills and mountains in historical rifts are capped by quartzite. It is much harder than the sandstone it originates from and will break through the quartz grains rather than around them.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. In the field, it often appears as rounded river cobbles or massive outcroppings with a sugary, granular appearance. Found globally in mountainous regions.
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