sedimentary and metamorphic

Quartzite / Sandstone / Chert Mix

Silicon Dioxide (SiO2)

Hardness of 7 on Mohs scale; colors range from opaque tan and beige to translucent white; dull to greasy/vitreous luster; non-foliated or clastic texture; very high resistance to weathering.

Identified March 24, 2026More sedimentary and metamorphic →

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Physical properties

Hardness of 7 on Mohs scale; colors range from opaque tan and beige to translucent white; dull to greasy/vitreous luster; non-foliated or clastic texture; very high resistance to weathering.

Formation & geological history

These specimens represent a mix of sedimentary sandstone and its metamorphic equivalent, quartzite. They formed from sand-sized grains of quartz cemented together and subsequently rounded through water erosion in riverbeds or coastal environments. They are typically hundreds of millions of years old.

Uses & applications

Common river stones are used industrially in construction as aggregate, landscaping, and sometimes in glass manufacturing if the quartz purity is high enough. Polished versions are used for aquarium decorative gravel.

Geological facts

Quartz is one of the most chemically and physically resistant minerals on Earth's surface, which is why these stones survive long journeys in rivers after softer rocks like limestone or shale have disintegrated.

Field identification & locations

Identify in the field by their inability to be scratched by a steel knife and their rounded 'river rock' shape. They are ubiquitous in riverbeds, glacial tills, and landscaping beds across the globe.

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Shale or Argillite

Shale (sedimentary) / Argillite (metamorphic)

Sedimentary or Metamorphic (low-grade)

Anthracite Coal

Anthracite (Carbon-rich Sedimentary-to-Metamorphic Rock)

metamorphic

Milky Quartz with Iron Inclusions

Quartz (Silicon Dioxide, SiO2)

mineral

Anthracite Coal

Anthracite (Carbon-based sedimentary-derived metamorphic rock)

metamorphic

Jasper Conglomerate (Puddingstone)

Siliceous Conglomerate (Quartz and Jasper clasts in a fine-grained matrix)

sedimentary

River Pebbles and Quartz

Mixed Igneous, Sedimentary, and Metamorphic Rocks (Silicon Dioxide SiO2 dominant)

mixed