igneous
Rounded gray river pebble, likely basalt or andesite
Fine-grained mafic/intermediate volcanic rock; likely basalt (plagioclase ± pyroxene, possibly iron oxides)
AI-generated identification · may be incorrectDark gray, fine-grained, dull to faintly satin luster, rounded and naturally water-worn; estimated Mohs hardness 5.5–6.5, with no visible cleavage or crystals. The pale patch may be a weathered feldspar-rich area or surface coating.
Identified More igneous →
Explore Rounded gray 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
Dark gray, fine-grained, dull to faintly satin luster, rounded and naturally water-worn; estimated Mohs hardness 5.5–6.5, with no visible cleavage or crystals. The pale patch may be a weathered feldspar-rich area or surface coating.
Formation & geological history
Formed from rapidly cooled lava, likely during the Cenozoic or earlier, then transported and smoothed by stream or beach abrasion. Exact identification and age require a fresh surface or laboratory testing.
Uses & applications
Common basaltic pebbles are used for landscaping, aggregate, drainage, and decorative stone; this small specimen has little commercial value unless locality or unusual texture is documented.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly forms oceanic crust. Its dark color reflects abundant iron- and magnesium-bearing minerals.
Field identification & locations
Look for a uniformly fine texture, dark gray-to-black color, high density, and lack of visible quartz; a streak, magnetism test, or fresh chip can help distinguish basalt from chert or slag. Common in volcanic terrains and gravel beaches worldwide.
