metamorphic
Quartzite (River Stone)
Quartzite
Hardness: 7 (Mohs scale); Color: Grayish-brown; Luster: Dull to vitreous when wet; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6-2.7. Highly durable and resistant to scratching.
- Hardness
- 7 (Mohs scale)
- Color
- Grayish-brown
- Luster
- Dull to vitreous when wet
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Physical properties
Hardness: 7 (Mohs scale); Color: Grayish-brown; Luster: Dull to vitreous when wet; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6-2.7. Highly durable and resistant to scratching.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone subjected to extreme heat and pressure. This specific grain-rounded shape indicates it was polished by water in a river or coastal environment.
Uses & applications
Commonly used in landscaping, as construction aggregate, for railroad ballast, and occasionally for primitive tools due to its hardness.
Geological facts
Quartzite is so hard that it can scratch glass and steel easily. It is often mistake for marble, but marble will react with acid and quartzite will not.
Field identification & locations
Identify in the field by its grainy, sandpaper-like texture (even when smooth) and its inability to be scratched by a steel knife. Found globally in riverbeds and mountainous glaciated regions.
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