metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan but can be colorful with impurities; Luster: Vitreous/waxy; Crystal Structure: Trigonal (as quartz); Cleavage: None; Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous/waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan but can be colorful with impurities; Luster: Vitreous/waxy; Crystal Structure: Trigonal (as quartz); Cleavage: None; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, forming an interlocking mosaic of quartz crystals.
Uses & applications
Used in construction as crushed stone for road gravel and rail ballast, in glass manufacturing, and as decorative dimension stone or kitchen countertops due to its durability.
Geological facts
Quartzite is so strong and dense that when struck with a rock hammer, it will break through the quartz grains rather than around them, unlike its parent rock, sandstone.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It often appears in rounded river cobbles or massive mountain ridges as it resists weathering.
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