metamorphic
Quartzite Cobble
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: tan to creamy white; Luster: dull to vitreous; Crystal structure: granular, non-foliated; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- tan to creamy white
- Luster
- dull to vitreous
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: tan to creamy white; Luster: dull to vitreous; Crystal structure: granular, non-foliated; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. The specimen shown is a water-rounded cobble typically found in fluvial or beach environments.
Uses & applications
Used in road construction, railroad ballast, decorative landscaping, and as an industrial source of silica.
Geological facts
Quartzite is harder and more durable than its parent rock, sandstone. It is so tough that it often breaks through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It often appears as rounded, smooth 'potatoes' on riverbanks or beaches.
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