Kidney stone. Coloured scanning electron micrograph (SEM) of the surface of a kidney stone or calculus. Such stones form in the kidneys when salt compounds precipitate out of the urine. This stone is formed from 20% calcium oxalate monohydrate and 80% calcium oxalate dihydrate. 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. Magnification: x165 at 6x7cm size. x250 at 4x5"~LANDSCAPE"