Resonant stones. Usually flat.
Etymology and Alternative Spellings
Playing stones can be found... use your ear as you play the rocks. Generally they should be about 2-3 inches in diameter and have a flat surface. River rock and other hard stones usually work the best, but experiment with what you have.
Make a small cup shape in one hand (as if holding water in the hand), place one stone in your hand over the cupped shape. Strike the body of the stone with the edge of the second stone, producing the most resonant sound possible. Experiment with the striking area until you find the best possible sound or the sound that creates the desired effect. You can change the pitch of the sound by manipulating the shape of the cup within your hand... less space equals a higher pitch; more space equals a lower pitch.