Illustration of a calculus or stone in the kidney. This staghorn stone, so-called for its branched shape (at centre, brown), lies within the renal pelvis and the calyces of the kidney. The larger blood vessels (red, blue) are the renal artery and vein. The adrenal gland is positioned above the kidney (yellow). Most kidney stones are made up of calcium salts, an end-product of body metabolism. Staghorn stones consist of calcium, magnesium, and ammonium phosphate. They are linked to chronic urinary tract infection in which the urine has a high ammonium content and alkalinity produced by the action of bacteria. Kidney stones may block the passage of urine down the ureter (white).