metamorphic
Quartzite River Rock
Quartzite (primarily SiO2)
Hardness: 7 on the Mohs scale; Color: Tan, beige, or yellowish-brown (due to iron stains); Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on the Mohs scale
- Color
- Tan, beige, or yellowish-brown (due to iron stains)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale; Color: Tan, beige, or yellowish-brown (due to iron stains); Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. High heat and pressure causes quartz grains to recrystallize. This specific smooth, rounded shape is the result of mechanical weathering and transport in high-energy water environments like riverbeds or coastal zones.
Uses & applications
Used as a decorative landscape stone, in construction as road ballast or concrete aggregate, and occasionally in glassmaking if the purity is high.
Geological facts
Quartzite is so hard that it can scratch glass and steel. It is often more durable than its parent rock (sandstone) and resists chemical weathering, which is why these stones often persist in riverbeds after other rocks have eroded away.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a knife) and its grainy, 'sugary' texture on a fresh break. Common in mountainous regions with a history of tectonic activity. Collectors often look for examples with unique weathering patterns or iron banding.
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