metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: white/grey; Luster: vitreous to grainy; crystal structure: Trigonal (as quartz); no cleavage; specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white/grey
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: white/grey; Luster: vitreous to grainy; crystal structure: Trigonal (as quartz); no cleavage; specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under intense heat and pressure, causing the original quartz grains to recrystallize into an interlocking mosaic.
Uses & applications
Used widely in construction as crushed stone, for road ballast, as a decorative dimension stone in countertops and walls, and in glassmaking if pure enough.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, remaining as prominent ridges or hilltops known as 'monadnocks'.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its grainy, granular look compared to milky quartz. Common in folded mountain belts.
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