metamorphic
Quartzite (River Pebble)
Quartzite (mainly SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, white, or gray; Luster: Vitreous to waxy when polished; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, white, or gray
- Luster
- Vitreous to waxy when polished
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, white, or gray; Luster: Vitreous to waxy when polished; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. This specific specimen has been rounded and smoothed by water erosion in a river or glacial environment.
Uses & applications
Commonly used as construction aggregate, railway ballast, and decorative landscaping stone. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so tough that it often survives intense weathering and erosion that destroys other rocks. It is harder than steel and will easily scratch a glass plate.
Field identification & locations
Identify by its extreme hardness and sugary or crystalline texture on a fresh break. It is found globally in areas of ancient mountain building. Collectors often look for colorful 'river bed' specimens for tumbling.
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