metamorphic
Quartzite
Metamorphic rock (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Structure: non-foliated, interlocking quartz grains; Cleavage: none (fractures conchoidally through grains)
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Structure: non-foliated, interlocking quartz grains; Cleavage: none (fractures conchoidally through grains)
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, individual quartz grains recrystallize into a dense, interlocking mosaic of crystals.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and building stone. Highly pure quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so durable that it often forms the crests of mountain ranges because it resists weathering far better than most other rocks. It is harder than steel and will scratch glass easily.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its habit of breaking through the sand grains rather than around them. Found globally in mountainous regions and ancient continental cratons.
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