metamorphic
Quartzite River Pebble
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Light grey, white, to tan; Luster: Vitreous to dull when weathered; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Light grey, white, to tan
- Luster
- Vitreous to dull when weathered
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Physical properties
Hardness: 7 on Mohs scale; Color: Light grey, white, to tan; Luster: Vitreous to dull when weathered; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone subjected to high heat and pressure, causing the original quartz grains to recrystallize. It is often found as a 'river pebble' after being tumbled and rounded by water action over thousands of years.
Uses & applications
Used in construction as crushed stone or road ballast, as a high-silica raw material for glass making, and occasionally as decorative landscaping stones or polishable tumbling material.
Geological facts
Quartzite is so durable that it often outlasts the mountain ranges from which it originated. It is harder than steel and will easily scratch a glass plate, which distinguishes it from similar-looking limestone or marble.
Field identification & locations
Identify in the field by its extreme hardness and grainy, sugary texture under a hand lens. It lacks the 'fizz' reaction to acid that carbonates have. Commonly found in riverbeds, glacial moraines, and eroded mountain belts globally.
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