metamorphic
Quartzite cobblestone
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Off-white to cream; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Off-white to cream
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white to cream; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing recrystallization. This specimen shows signs of river or coastal erosion (rounded edges).
Uses & applications
Used as a construction aggregate, for road ballast, as a decorative garden stone, or in glass manufacturing if highly pure.
Geological facts
Quartzite is significantly harder and more durable than the sandstone it originates from. It is often so tough that it breaks through the quartz grains rather than around them.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture. Commonly found in riverbeds or ancient glacial deposits.
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