metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish due to iron staining; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or yellowish due to iron staining
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish due to iron staining; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing quartz grains to recrystallize and fuse together. Most deposits are hundreds of millions to billions of years old.
Uses & applications
Used in construction as crushed stone for road gravel and rail ballast, in glass manufacturing, and occasionally as decorative stone or building facades.
Geological facts
Quartzite is so hard and durable that it often forms the peaks of mountain ranges because it resists erosion better than surrounding rocks. It can be distinguished from sandstone because it fractures through the grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Commonly found in folded mountain belts. Collectors look for high-purity specimens or those with interesting inclusions.
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