igneous and sedimentary
River Stones (Basalt and Sedimentary Rock)
Basalt (dark specimen) and Siltstone/Mudstone (reddish specimen)
Hardness: 5-7 (Mohs scale), Color: Dark grey to reddish-brown, Luster: Dull to waxy when wet, Texture: Fine-grained and smooth due to water erosion.
Identified More igneous and sedimentary →
Explore River Stones (Basalt and Sedimentary Rock) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-7 (Mohs scale), Color: Dark grey to reddish-brown, Luster: Dull to waxy when wet, Texture: Fine-grained and smooth due to water erosion.
Formation & geological history
Formed through volcanic activity (basalt) or the accumulation of fine particles (sedimentary). These specific smooth shapes are the result of mechanical weathering and transport by river or stream water over thousands of years.
Uses & applications
Commonly used in landscaping, decorative ground cover, aquarium substrates, and increasingly in hot stone massage therapies.
Geological facts
The smooth, rounded shape is a classic example of fluvial abrasion, where rocks tumble against one another in moving water, wearing down sharp edges.
Field identification & locations
Identify by their rounded, egg-like shapes and smooth surfaces. Found globally in active or ancient riverbeds and along shorelines.
More like this
Other igneous and sedimentary specimens
Quartz (Druzy)
Silicon Dioxide (SiO2)
mineral
Botryoidal Chalcedony
Chalcedony (SiO2)
Mineral
Greenstone (Greywacke or Nephrite Jade variant)
Metamorphosed mafic igneous or sedimentary rock (e.g., Actinolite-Chlorite Schist)
metamorphic
Quartz (Chalcedony/Agate)
Silicon Dioxide (SiO2)
mineral
Quartz
Silicon Dioxide (SiO2)
Mineral
Ruby Zoisite
Anyolite (Calcium aluminium silicate with Chromium/Corundum inclusions)
metamorphic