metamorphic
Quartzite Cobble
Quartzite (primarily SiO2)
AI-generated identification · may be incorrectHardness: 7 on Mohs scale; Color: Grey, black, and dull red/pink; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grey, black, and dull red/pink
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey, black, and dull red/pink; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure. The rounded shape indicates extensive water erosion in a high-energy environment like a river or beach.
Uses & applications
Used in construction as road ballast, gravel, and building stone. Highly weathered specimens are mostly of interest to amateur geologists and for landscaping.
Geological facts
Quartzite is so hard and chemically resistant that it often outlasts the surrounding rocks, remaining as rounded cobbles long after other minerals have weathered away.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by steel) and lack of visible grains compared to sandstone. Commonly found in glaciated regions, riverbeds, and coastal areas.
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