metamorphic
Quartzite pebble
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: light grey/tan, Luster: dull to vitreous, Crystal structure: Trigonal/Hexagonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey/tan, Luster: dull to vitreous, Crystal structure: Trigonal/Hexagonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, often during mountain-building events. This specimen has been further rounded by water or glacial transport.
Uses & applications
Used primarily as construction aggregate, railway ballast, and in road styling. Highly rounded pebbles are used in landscaping and aquariums.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, remaining as rounded pebbles in riverbeds millions of years after its parent formation has eroded away.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Commonly found in riverbeds, glacial tills, and along coastal beaches.
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