metamorphic
Quartzite Pebble
Metamorphic Quartzite
Hardness: 7 on the Mohs scale. Color: Light gray, white, or off-white. Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline quartz grains fused together). Cleavage: None, breaks with a conchoidal fracture. Specific gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Light gray, white, or off-white
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on the Mohs scale. Color: Light gray, white, or off-white. Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline quartz grains fused together). Cleavage: None, breaks with a conchoidal fracture. Specific gravity: 2.65.
Formation & geological history
Formed from quartz-rich sandstone subjected to high heat and pressure during regional or contact metamorphism. The original quartz grains recrystallize and interlock tightly. Geological age can range from Precambrian to Cenozoic.
Uses & applications
Used in construction, as road aggregate, railroad ballast, and in the manufacturing of silica brick and ferroalloys. Also used as decorative landscaping stone.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why quartz-rich rocks often survive as pebbles in rivers and beaches long after other rocks have eroded away.
Field identification & locations
Can be identified by its inability to be scratched by a steel knife (hardness > 5.5) and the sugary, glittering texture of fractured surfaces where individual quartz crystals break rather than pulling apart between grains. Commonly found in riverbeds, glacial tills, and mountainous metamorphic terrains worldwide.
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