sedimentary

Quartz River Pebbles

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: typically white, tan, grayish, or milky; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (though not visible in rounded pebbles); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: typically white, tan, grayish, or milky
Luster: Vitreous to waxy

Identified March 30, 2026More sedimentary →

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Physical properties

Formation & geological history

These specimens are detrital sedimentary rocks formed through the mechanical weathering of larger igneous or metamorphic parent rocks. Over a periods ranging from thousands to millions of years, they were transported by water currents, which rounded them through abrasion in riverbeds or coastal environments.

Uses & applications

Used in landscaping, construction aggregate, aquarium decor, and sometimes in industrial grinding processes. High-purity quartz pebbles can be used in the glass-making industry.

Geological facts

River pebbles are excellent indicators of the tectonic history of a region; their composition often mirrors the geology of the mountains upstream from where they were found. Quartz is one of the most chemically stable minerals at the Earth's surface, which is why it predominates in these types of deposits.

Field identification & locations

Identify in the field by their smooth, rounded 'potato-like' shapes and high hardness (they will scratch glass). They are ubiquitous in current and ancient riverbeds, alluvial fans, and beaches worldwide. For collectors, they represent the basic cycle of erosion and deposition.