metamorphic
Quartzite Cobble
Quartzite (predominantly SiO2)
Hardness: 7 (Mohs scale); Color: tan, brownish-grey; Luster: vitreous to dull; Crystal structure: granular/clastic texture; Cleavage: none (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Color
- tan, brownish-grey
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: tan, brownish-grey; Luster: vitreous to dull; Crystal structure: granular/clastic texture; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed via regional metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events. This specimen has been rounded by fluvial (water) erosion.
Uses & applications
Used in construction as road ballast, railway ballast, and as a durable material for stone walls or landscaping. Fine varieties are used in glass manufacturing.
Geological facts
Quartzite is one of the hardest and most chemically resistant rocks on Earth's surface. It often forms the resistant caps of ridges because it outlasts surrounding softer rocks like shale or limestone.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and granular, sugary appearance on a fresh break. Commonly found in riverbeds, glacial tills, and mountainous metamorphic belts.
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