What is a kidney stone?

A kidney stone is a hard mineral and crystalline material formed within the kidney or urinary tract. A kidney stone is also a solid piece of material that forms from crystallization of excreted substances in the urine. The stone may remain in the kidney or break loose and travel down the urinary tract. A small stone may pass all of the way out of the body, but a larger stone can get stuck in a ureter, the bladder, or the urethra. This may block the flow of urine and cause great pain.

A kidney stone may be as small as a grain of sand or as large as a pearl, and some are as big as golf balls. Approximately 80 percent of kidney stones are less than 2 centimeters in width. They may be smooth or jagged, and are usually yellow or brown in color.

Kidney stones are a common cause of blood in the urine and often severe pain in the abdomen, flank, or groin. Kidney stones are sometimes called renal calculi. One in every 20 people develops a kidney stone at some point in their life.The condition of having kidney stones is termed nephrolithiasis or urolithiasis. (healthsystem.virginia.edu)