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.
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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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