metamorphic
Quartzite Pebble
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Light tan/gray; Luster: Dull to vitreous; Crystal structure: Trigonal/hexagonal (microcrystalline); Cleavage: None; Specific gravity: 2.6–2.7
- Hardness
- 7 (Mohs scale)
- Color
- Light tan/gray
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Light tan/gray; Luster: Dull to vitreous; Crystal structure: Trigonal/hexagonal (microcrystalline); Cleavage: None; Specific gravity: 2.6–2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, where individual quartz grains recrystallize together. This process typically occurs during mountain-building events.
Uses & applications
Commonly used in construction as crushed stone, for railroad ballast, or as decorative landscaping stones. In ancient times, it was used for stone tools.
Geological facts
Quartzite is one of the most physically and chemically resistant rocks on the Earth's surface. When it breaks, it breaks through the quartz grains rather than along their boundaries.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in riverbeds or near mountain ranges where erosion has weathered away softer surrounding rocks.
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