metamorphic
Quartzite Pebble
Quartzite (SiO2) with mineral inclusions
Hardness: 7 on Mohs scale; Color: Tans, grays, and oranges from iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, fractures conchoidally.
- Hardness
- 7 on Mohs scale
- Color
- Tans, grays, and oranges from iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tans, grays, and oranges from iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, fractures conchoidally.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism). The rounded shape is the result of fluvial (river) or glacial erosion over thousands of years.
Uses & applications
Used primarily as construction aggregate, ballast for railroads, and decorative landscaping stones. Smooth pebbles are often used in decorative fountains or as tumbling media.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, remaining as pebbles and boulders long after the parent rock has weathered away.
Field identification & locations
Identify by its hardness (it will scratch glass) and its grainy, sugary texture visible under a loupe. It often lacks the banding seen in chert or agate. Found globally in riverbeds and beaches.
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