metamorphic
Quartzite Pebble
Quartzite (SiO2)
Hardness: 7 on the Mohs scale. Color: Tan, brown, or yellowish due to iron oxide staining. 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
- Tan, brown, or yellowish due to iron oxide staining
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on the Mohs scale. Color: Tan, brown, or yellowish due to iron oxide staining. 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 through the metamorphism of quartz sandstone or chert under high heat and tectonic pressure, commonly over hundreds of millions of years.
Uses & applications
Used in construction, railroad ballast, crushed stone, decorative landscaping, and sometimes for lapidary work.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why quartz-rich rocks often survive as smooth, rounded pebbles in rivers and beaches long after other rocks have eroded away.
Field identification & locations
Found worldwide in stream beds, ancient river terraces, and glacial outwash. It can be identified by its inability to be scratched by steel and its lack of effervescence with acid.
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