Picture of Kidney Stone Crystal
Kidney stones are hard, sometimes jagged crystals made up of different solids that form in the kidneys. Kidney stones may be made of calcium, oxalate, phosphate, or other substances. Small stones may travel easily down the ureter and be expelled by the body in the urine. Larger stones may block the flow of urine and cause severe pain. Pain associated with kidney stones is often felt in the abdomen, groin, or the flank area. About 5% of people develop a kidney stone at some point in life.
Text Reference: "Kidney Stones." National Kidney Foundation.