Kidney stones are deposits of mineral salts, called calculi, in the kidney. These stones can pass into the ureter, the narrow tube that connects the kidneys to the bladder.
Kidney stones occur when the urine has a high level of minerals that form stones.
Most kidney stones are made from calcium. Minerals such as uric acid and oxalate may also form stones. These stones can irritate kidney tissue and block urine flow. Some stones can grow to be very large without causing symptoms. Flank pain is a common symptom of kidney stones.