metamorphic
Quartzite Pebble
Metamorphic Quartzite
Hardness: 7 on the Mohs scale. Color: Tan, brown, white, and reddish hues. Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline quartz grains fused together). Cleavage: None, fractures conchoidally. Specific gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Tan, brown, white, and reddish hues
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on the Mohs scale. Color: Tan, brown, white, and reddish hues. Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline quartz grains fused together). Cleavage: None, fractures conchoidally. Specific gravity: 2.65.
Formation & geological history
Formed from quartz-rich sandstone or chert that has been subjected to high heat and pressure, typically during tectonic mountain-building events (regional metamorphism). Geological age varies widely from Precambrian to Cenozoic.
Uses & applications
Used in construction, road aggregate, railway ballast, manufacturing of silica bricks, and occasionally as decorative landscaping stones or tumbled polished pocket stones.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why quartz-rich rocks often survive as rounded pebbles in rivers and beaches long after less durable minerals have worn away.
Field identification & locations
Can be identified in the field by its high hardness (it easily scratches glass and cannot be scratched by a steel knife) and the way it breaks across individual quartz grains rather than around them, unlike sandstone. Commonly found in riverbeds, glacial tills, and ancient sedimentary basins worldwide.
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