metamorphic
Quartzite
Quartzite (High-purity SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or brownish; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.65
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or brownish
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or brownish; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.65
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, where quartz grains recrystallize and fuse together. Often found in orogenic (mountain-building) belts.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the production of glass and industrial abrasives.
Geological facts
Quartzite is so tough that it often breaks through the constituent quartz grains rather than around them, which distinguishes it from sandstone. Some varieties can contain impurities that create vibrant pink, red, or yellow hues.
Field identification & locations
Look for a sugary texture that cannot be scratched by a steel knife. It is common in ancient mountain ranges like the Appalachians or the Alps. Collectors should look for rare colored variants or those with interesting mineral inclusions.
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