metamorphic
Quartzite
Quartzite (composed primarily of Silica, SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, or tan; Luster: vitreous to fatty; Structure: crystalline/granular; Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- white, gray, or tan
- Luster
- vitreous to fatty
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, or tan; Luster: vitreous to fatty; Structure: crystalline/granular; Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize into a silica-cemented interlocking network of quartz crystals.
Uses & applications
Used as a decorative stone in landscaping, a dimension stone in construction (countertops and flooring), and crushed stone for road grit or railway ballast.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks; it forms the caps of many mountain ranges because it resists weathering so effectively. It is much harder and more durable than the sandstone it originated from.
Field identification & locations
Identified in the field by its hardness (it will easily scratch glass) and the way it breaks: unlike sandstone where grains break around each other, quartzite breaks through the quartz grains. Look for a sugary, crystalline texture on fresh surfaces.
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