metamorphic
Quartzite (River Stone)
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white, grey, and tan with iron staining; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Off-white, grey, and tan with iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white, grey, and tan with iron staining; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the sand grains to recrystallize into a dense, interlocking matrix. This specimen shows significant rounding from river transport.
Uses & applications
Used in construction as crushed stone, railway ballast, and as a decorative landscaping stone. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks. It is harder than a steel knife blade and can easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and sugary, crystalline appearance on fresh surfaces. It is commonly found in riverbeds, glacial tills, and ancient mountain belts.
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