metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, brownish-buff (shown here), or reddish; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, brownish-buff (shown here), or reddish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, brownish-buff (shown here), or reddish; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The individual quartz grains recrystallize into a locked mosaic.
Uses & applications
Used as a crushed stone in construction, road ballast, and as a raw material for glass and ceramics. High-quality slabs are used for countertops and ornamental flooring.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming high ridges and mountains. It is differentiateable from sandstone because it breaks through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Look for a sugary, granular appearance with a smooth, almost glassy fracture surface. Commonly found in folded mountain belts worldwide.
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