Ordinary Pebble (Underwater Cave)

This Ordinary Pebble is found above water at in an underwater cave off the western coast of Boralus. It is part of the Riddle of Baa'l.

The cave mouth is at (using Boralus coordinates). Head into one of the Cataclysm-era caves and travel south to poke out of the water. On the right-hand side of the exposed land (on the western side of the cave), the pebble is covered by some kelp.

Solution
Next and final pebble is located way off the northern coast of Zandalar.