metamorphic
Quartzite Pebble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Light gray to tan with faint white veins; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- Light gray to tan with faint white veins
- Luster
- Vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: Light gray to tan with faint white veins; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with conchoidal fracture.
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, which causes the individual quartz grains to recrystallize into a dense, interlocking mosaic of crystals.
Uses & applications
Used in construction as a decorative stone, road ballast, and in the production of glass and ferrosilicon. Smooth pebbles are popular for landscaping and home decor.
Geological facts
Quartzite is so tough that it often survives intense weathering and erosion that destroys other rocks, resulting in the rounded river pebbles like the one shown. It is harder than steel.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and its grainy but fused appearance. Commonly found in riverbeds, glacial deposits, and mountain ranges.
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