metamorphic
Quartzite
Metaquartzite (predominantly SiO2)
AI-generated identification · may be incorrectHardness: 7 on the Mohs scale; Color: Pinkish-purple to reddish-brown; Luster: Vitreous to dull/sugary; Cleavage: None (conchoidal to uneven fracture across grains); Specific Gravity: 2.6 - 2.7
- Hardness
- 7 on the Mohs scale
- Color
- Pinkish-purple to reddish-brown
- Luster
- Vitreous to dull/sugary
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Physical properties
Hardness: 7 on the Mohs scale; Color: Pinkish-purple to reddish-brown; Luster: Vitreous to dull/sugary; Cleavage: None (conchoidal to uneven fracture across grains); Specific Gravity: 2.6 - 2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone subjected to high heat and pressure, causing original quartz grains to recrystallize and fuse into a dense, interlocking matrix. This rounded cobble exhibits surface smoothing from glacial transport or water erosion.
Uses & applications
Commonly used as construction aggregate, railway ballast, dimension stone, riprap for erosion control, and occasionally cut/polished for decorative stone landscaping.
Geological facts
Unlike sandstone, which breaks around individual sand grains leaving a rough surface, quartzite is so strongly fused that it fractures directly through the quartz grains. Prominent pink-to-purple varieties, such as the famous Baraboo Quartzite in Wisconsin, owe their coloration to trace iron oxide (hematite) inclusions.
Field identification & locations
Identifiable by its extreme hardness (scratches glass with ease and cannot be scratched by steel), granular sugary texture with sparkling reflective quartz facets, and resistance to chemical weathering. Commonly found in glaciated terrains, riverbeds, and ancient deformed mountain belts.
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