pebble
Definitions
A small, smooth stone, especially one worn round by the action of water.
A small, rounded rock or mineral fragment, typically larger than a grain of sand and smaller than a cobble.
Examples
She skipped a smooth pebble across the surface of the lake.
I felt a sharp pebble inside my shoe while walking on the beach.
The garden path was lined with a decorative border of white pebble.