metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on the Mohs scale. Color: white, gray, or tan. Luster: Vitreous to dull. Crystal Structure: Hexagonal (trigonal). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6 - 2.7.
- Hardness
- 7 on the Mohs scale
- Color
- white, gray, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: white, gray, or tan. Luster: Vitreous to dull. Crystal Structure: Hexagonal (trigonal). Cleavage: None (conchoidal fracture). 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 and fuse together, creating a hard, interlocking network.
Uses & applications
Used widely in construction as decorative stone, crushed stone for road gravel and railroad ballast, in the production of glass and silicon, and as high-end countertops.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the crests of ridges and hills, as it resists erosion much better than the surrounding softer rocks.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and sugary/granular appearance that breaks across grains rather than around them. Found globally in ancient mountain belts.
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