metamorphic
Quartzite pebble
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, cream, or light grey; Luster: Dull to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None, fractures conchoidally; Specific Gravity: 2.6-2.65.
- Hardness
- 7 (Mohs scale)
- Color
- White, cream, or light grey
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: White, cream, or light grey; Luster: Dull to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None, fractures conchoidally; Specific Gravity: 2.6-2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under extreme heat and pressure, which causes the individual quartz grains to recrystallize into a locked mosaic. This specific specimen is a 'river stone' or 'beach pebble,' smoothed by water erosion over many years.
Uses & applications
Commonly used in landscaping, decorative gravel, construction aggregate, and occasionally as a source of silica for industrial glass making. Tumbled specimens are popular for home decor or 'worry stones'.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks; it is much harder than the sandstone it originated from and will scratch glass and steel easily. It is often confused with marble, but quartzite is much harder and will not react to acid.
Field identification & locations
Identify in the field by its hardness (scratching glass) and lack of reaction to vinegar/acid. Look for a sugary texture on broken surfaces. Very common in riverbeds, glacial tills, and mountainous regions worldwide.
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