The medical term for this condition is nephrolithiasis , or renal stone disease. Kidney stones may be as small as a grain of sand or larger than a golf ball. They may be smooth, round, jagged, spiky, or asymmetrical, depending on their composition. Most stones are yellow or brown in color, but variations in chemical composition can produce stones that are tan, gold, or black.
Some stones stay in the kidney and produce no symptoms.
Other stones break loose and travel down the urinary tract. The smallest, smoothest stones may pass out of the body with little resistance, and the patient may experience minimal discomfort. A lodged stone can block the flow of urine, causing waste and pressure to build up in the kidneys. Such a condition must be corrected swiftly to prevent serious kidney damage and other medical problems. The stone can be removed surgically, or can be broken up and then passed naturally out of the body.