Kidney stone shock wave treatment. Illustration of extracorporeal shock wave lithotripsy (ESWL) being carried out as a non-invasive treatment of a kidney stone. The kidney stone is shattered into small fragments by high-energy shock waves represented by the beam (green). Kidney stones are usually formed by the precipitation of the mineral salt calcium oxalate from the urine. The resulting hard, round stones (calculi) may cause severe pain, especially as they pass down the urinary tract.