metamorphic
Quartzite River Cobble
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Creamy white to light gray with iron staining; Luster: Dull to waxy; Structure: Granular/crystalline; Cleavage: None/conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Creamy white to light gray with iron staining
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Creamy white to light gray with iron staining; Luster: Dull to waxy; Structure: Granular/crystalline; 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. This specific specimen has been rounded and smoothed by mechanical weathering in a high-energy aquatic environment, such as a riverbed or coastal area.
Uses & applications
Commonly used in landscaping (river rock), construction aggregate, and occasionally as a source of silica for glassmaking.
Geological facts
Quartzite is so durable that it often survives intense weathering that destroys other rocks. While sandstone breaks around the sand grains, quartzite breaks through them because the crystals are so tightly interlocked.
Field identification & locations
Identify by its extreme hardness (it will easily scratch glass) and its sugary, crystalline surface texture. Found globally in ancient riverbeds and processed for decorative landscaping.
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