Scanning electron micrograph (SEM) of a kidney stone, composed of calcium-oxalate crystals. Such stones form in the kidneys when salt compounds precipitate out of the urine. Small kidney stones cause no problems, but if they grow they can damage the kidney and impair its function. If they pass into either of the ureters, (the tubes which carry urine to the bladder) they can cause severe pain, fever and damage. In these cases, the stones can be surgically removed or fragmented using ultrasound waves. Width of SEM: 63.3 micrometers (stone 20 micrometers).
