Kidney stones are crystals of dissolved minerals in urine which are found inside the urinary system. They vary in sizes from as small as a grain of sand to as large as a golf ball. They are formed from the dissolved minerals in urine. As the kidney produces urine and flushes the urinary system, there is a tendency for the stones to move and to pass out through the urinary tract.
Sometimes, when the crystals or stones become too large (about 2–3mm), they will obstruct the urine stream and cause acute pain during urination. As the stone rubs against the inner lining of the urinary tract, it can damage the tract and cause blood to flow into the urine. The injured site can become a nidus (or catalyst) for recurrent urinary infection. At times, the stones can cause kidney damage and failure due to recurrent infection and obstruction.