A kidney stone, also known as a renal calculus or nephrolith, is a solid piece of material which is formed in the kidneys from minerals in urine. Kidney stones typically leave the body in the urine stream, and a small stone may pass without causing symptoms. If stones grow to sufficient size (usually at least ) they can cause blockage of the ureter. This leads to pain, most commonly beginning in the flank or lower back and often radiating to the groin. This pain is often known as renal colic and typically comes in waves lasting 20 to 60 minutes. Other associated symptoms include: nausea, vomiting, fever, blood in the urine, pus in the urine, and painful urination. Blockage of the ureter can cause decreased kidney function and dilation of the kidney.