igneous and sedimentary

River Pebbles (Tumbled Quartz and Basalt)

Silicon Dioxide (SiO2) for white quartz; Mafic Volcanic Rock for basalt

AI-generated identification · may be incorrect

Hardness: 6-7 Mohs; Color: Creamy white (quartz) and dark grey/black (basalt); Luster: Sub-vitreous to dull; Structure: Microcrystalline/Aphanitic; Cleavage: None/Conchoidal

Hardness: 6-7 Mohs
Color: Creamy white (quartz) and dark grey/black (basalt)
Luster: Sub-vitreous to dull

Identified March 23, 2026More igneous and sedimentary →

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Physical properties

Hardness: 6-7 Mohs; Color: Creamy white (quartz) and dark grey/black (basalt); Luster: Sub-vitreous to dull; Structure: Microcrystalline/Aphanitic; Cleavage: None/Conchoidal

Formation & geological history

Formed through cooling magma (basalt) or hydrothermal veins (quartz). These specimens have been weathered and smoothed by mechanical abrasion in a river or beach environment over thousands of years.

Uses & applications

Used in landscaping, decorative stone for gardens, massage therapy (basalt), and as tumbled stones for amateur geological collections.

Geological facts

River rocks are often shaped into 'ellipsoids' due to the uniform tumbling action of water. Basalt is the most common rock in the Earth's crust, making up most of the ocean floor.

Field identification & locations

Identify by their smooth, rounded edges and lack of sharp corners. Common in stream beds, glacial deposits, and coastlines. Collectors look for unique colors or perfectly symmetrical oval shapes.