igneous
Rounded gray pebble, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; commonly plagioclase with pyroxene and/or olivine
AI-generated identification · may be incorrectHardness about 5.5–6.5 Mohs; gray, dull to faintly granular luster, compact texture, and no visible cleavage or crystals at this scale. Its smooth, flattened shape indicates water or beach abrasion; exact identification requires a fresh surface or testing.
Identified More igneous →
Explore Rounded gray pebble, likely basalt or andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness about 5.5–6.5 Mohs; gray, dull to faintly granular luster, compact texture, and no visible cleavage or crystals at this scale. Its smooth, flattened shape indicates water or beach abrasion; exact identification requires a fresh surface or testing.
Formation & geological history
Likely formed from rapidly cooled lava, then rounded by erosion in a stream, lake, or shoreline environment. The rock may be millions to hundreds of millions of years old, depending on its source.
Uses & applications
Suitable mainly as a decorative pebble, paperweight, landscaping stone, or lapidary material; ordinary specimens have little industrial or jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly forms oceanic crust and extensive lava flows.
Field identification & locations
Look for a dark gray fine-grained interior, high density, lack of layering, and possible tiny feldspar crystals; a streak, magnetism, acid, and thin-section test can distinguish basalt from andesite or other pebbles. Common worldwide, especially volcanic regions and riverbeds.
