metamorphic
Quartzite (River Pebble)
Metamorphosed Quartz-rich Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, white, or light brownish; Luster: Vitreous to waxy; Structure: Granular/crystalline; Cleavage: None (conchoidal fracture); High durability.
- Hardness
- 7 on Mohs scale
- Color
- Tan, white, or light brownish
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, white, or light brownish; Luster: Vitreous to waxy; Structure: Granular/crystalline; Cleavage: None (conchoidal fracture); High durability.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under high heat and pressure, typically in orogenic (mountain-building) belts. This specific specimen has been further shaped and rounded by fluvial (river) erosion over thousands of years.
Uses & applications
Commonly used as decorative landscaping stone (river rock), railway ballast, road construction, and occasionally in glassmaking if pure enough.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, remaining as rounded pebbles in creek beds long after other minerals have dissolved. It is one of the hardest common rocks found in nature.
Field identification & locations
Identify by its ability to scratch glass and its grainy, sugary appearance despite being smooth to the touch. Found globally in riverbeds, glacial deposits, and decorative gravel pits.
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