igneous
Rounded gray river pebble
Likely fine-grained basalt or andesite; exact identification requires testing
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to faintly satin luster, smooth water-worn surface, with no visible crystals or cleavage. Estimated Mohs hardness 5.5–6.5 and specific gravity about 2.7–3.0.
Identified More igneous →
Explore Rounded gray river pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-green, fine-grained, dull to faintly satin luster, smooth water-worn surface, with no visible crystals or cleavage. Estimated Mohs hardness 5.5–6.5 and specific gravity about 2.7–3.0.
Formation & geological history
Probably an eroded volcanic cobble transported and rounded by stream or wave action; its geological age cannot be determined from the photograph and depends on its source terrain.
Uses & applications
Primarily a natural decorative or landscaping stone, paperweight, or teaching specimen; generally unsuitable for jewelry unless cut and polished.
Geological facts
The rounded shape and smooth cortex indicate prolonged abrasion during transport. A magnet, streak, acid, and fresh-break tests would help distinguish basalt from other dark rocks.
Field identification & locations
Common in riverbeds, beaches, glacial deposits, and volcanic regions. Basalt is typically dense, nonlayered, and may contain tiny feldspar or pyroxene grains; andesite is usually slightly lighter and often porphyritic.
