igneous
Dark river pebble (likely basalt or andesite)
Fine-grained mafic/intermediate volcanic rock; commonly basalt (plagioclase ± pyroxene/olivine)
AI-generated identification · may be incorrectSmooth, rounded, dark gray-green pebble with dull to slight waxy luster; likely Mohs 5–6, non-cleavable, fine-grained, and relatively dense (about 2.7–3.1 g/cm³). The photograph does not show enough detail for definitive identification.
Identified More igneous →
Explore Dark river pebble (likely basalt or andesite) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Smooth, rounded, dark gray-green pebble with dull to slight waxy luster; likely Mohs 5–6, non-cleavable, fine-grained, and relatively dense (about 2.7–3.1 g/cm³). The photograph does not show enough detail for definitive identification.
Formation & geological history
Likely weathered and water-rounded from volcanic rock, possibly Quaternary to older depending on source terrain; basalt forms when lava cools rapidly at or near Earth’s surface.
Uses & applications
Used as decorative landscaping stone, aggregate, riprap, and occasionally as a tumbled or polished ornamental specimen; not typically a gemstone.
Geological facts
Basalt is the most common volcanic rock and forms much of the oceanic crust. A magnet may show weak attraction if the pebble contains abundant magnetite.
Field identification & locations
Look for a uniformly fine texture, dark color, high density, and absence of visible grains; a streak test, magnet test, and fresh broken surface help distinguish basalt from glassy slag or dark sedimentary rocks. Common worldwide near volcanic terrains and riverbeds.
