igneous and sedimentary
River Rocks (Basalt and Sedimentary Stones)
Mafic Igneous Rock (Basalt) and Clastic Sedimentary Rock
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
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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.
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