metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: tan, white, or light grey; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None, breaks with conchoidal or irregular fracture; Specific gravity: 2.6 to 2.7.
- Hardness
- 7 on Mohs scale
- Color
- tan, white, or light grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, white, or light grey; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None, breaks with conchoidal or irregular fracture; Specific gravity: 2.6 to 2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, typically in mountain-building (orogenic) environments.
Uses & applications
Used as a decorative stone in landscaping, a durable construction aggregate, for railroad ballast, and occasionally in glassmaking if high purity. Smooth river-worn specimens are often used for meditation stones or paperweights.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in the landscape, forming ridges and mountain peaks. Unlike sandstone, which breaks around its grains, quartzite breaks through its grains.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and grainy appearance. Commonly found along riverbeds or in mountainous regions with exposed metamorphic basement rock. This specific piece is a water-worn river cobble.
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