igneous and sedimentary

River Rocks (Basalt and Sedimentary Stones)

Mafic Igneous Rock (Basalt) and Clastic Sedimentary Rock

AI-generated identification · may be incorrect

Hardness: varies 5-7 (Mohs); Color: dark gray, light gray, tan-brown; Luster: dull to earthy; Texture: fine-grained to phaneritic

Hardness: varies 5-7 (Mohs)
Color: dark gray, light gray, tan-brown
Luster: dull to earthy

Identified May 21, 2026More igneous and sedimentary →

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Physical properties

Hardness: varies 5-7 (Mohs); Color: dark gray, light gray, tan-brown; Luster: dull to earthy; Texture: fine-grained to phaneritic

Formation & geological history

The dark specimen (left) is an igneous basalt formed from cooling lava. The rounded specimens (center/right) are sedimentary stones that have been weathered and smoothed over time by water transport in river or coastal environments.

Uses & applications

Used primarily in landscaping, decorative ground cover, aquarium substrate, and as aggregate in construction and road building.

Geological facts

River rocks are geological travelers; their smoothness is a direct record of the distance and intensity of hydraulic energy they have endured during transport.

Field identification & locations

Identify by the smooth, rounded 'water-worn' edges on the right two specimens and the fine-grained, dark mafic appearance of the basalt on the left. Highly common in riverbeds and glacial deposits worldwide.