metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or brown when weathered; Luster: vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or brown when weathered
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or brown when weathered; Luster: vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events. Geological age varies widely from Precambrian to Cenozoic.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a raw material in the glass and ceramics industries. Hard-wearing varieties are used for countertops and flooring.
Geological facts
Quartzite is so tough that it often survives intense erosion to form the tops of ridges and mountains. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and a sugary, granular appearance on fresh breaks. It is found globally in folded mountain belts. Collectors look for high-purity or uniquely colored specimens.
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