metamorphic
Quartzite Cobble
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: brown to tan due to iron staining; Luster: dull to waxy; Texture: granular, non-foliated; Structure: crystalline; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- brown to tan due to iron staining
- Luster
- dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: brown to tan due to iron staining; Luster: dull to waxy; Texture: granular, non-foliated; Structure: crystalline; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specimen has been rounded into a 'cobble' through fluvial (river) or glacial abrasion over thousands of years.
Uses & applications
Used as aggregate in construction, road ballast, and decorative landscaping. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, frequently forming the resistant caps of ridges and mountains.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its rounded, smooth surface if found in riverbeds. Common in ancient glacial till and high-energy river systems.
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