metamorphic
Quartzite Cobble
Quartzite (Silicon Dioxide, SiO2)
AI-generated identification · may be incorrectHardness: 7 on Mohs scale; Color: Tan, beige, or off-white; Luster: Dull to vitreous; Structure: Granoblastic (crystalline); Specific gravity: 2.6-2.7. Extremely durable and resistant to scratching.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or off-white
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or off-white; Luster: Dull to vitreous; Structure: Granoblastic (crystalline); Specific gravity: 2.6-2.7. Extremely durable and resistant to scratching.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism), causing quartz grains to recrystallize and fuse together. These rounded cobble shapes are created by water erosion in rivers or coastal environments.
Uses & applications
Used as construction aggregate, railway ballast, decorative landscaping stone, and historically as a tool stone for making strike-a-lights or simple grinders.
Geological facts
Quartzite is so tough that it often breaks through the quartz grains rather than along the boundaries between them, unlike its parent sandstone. It is one of the most chemically and physically resistant rocks on Earth's surface.
Field identification & locations
Identify by its inability to be scratched by a steel knife (hardness) and its sugary, crystalline texture upon a fresh break. Commonly found in riverbeds, glacial tills, and ancient mountain belts.
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