metamorphic
Quartzite
Quartzite (Primary mineral: SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white to tan; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white to tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white to tan; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the regional metamorphism of quartz sandstone. Intense heat and pressure cause quartz grains to recrystallize and fuse together. Found in many geological ages from Precambrian to Mesozoic.
Uses & applications
Used as road ballast, railway track bedding, decorative stone in landscaping, and sometimes as dimension stone for flooring or countertops due to its extreme durability.
Geological facts
Quartzite is so tough that it often forms the resistant ridges and hilltops of mountain ranges because it weathers much more slowly than surrounding rocks. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it cannot be scratched by a knife). Common in fold mountain belts worldwide. Collectors look for pieces with interesting mineral inclusions or crystal pockets.
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