Urine has many dissolved minerals and salts. When your urine has high levels of these minerals and salts, you can form stones. Kidney stones can start small but can grow larger in size, even filling the inner hollow structures of the kidney. Some stones stay in the kidney, and do not cause any problems. Sometimes, the kidney stone can travel down the ureter, the tube between the kidney and the bladder. If the stone reaches the bladder, they pass out of the body in urine. If the stone becomes lodged in the ureter, it blocks the urine flow from that kidney and causes pain. Kidney stones come in many different types and colours. How you treat them and stop new stones from forming depends on what type of stone you have. They might be calcium stones, uric acid stones and rarely cysteine stones.