Cesium is a soft, silvery-golden alkali metal naturally present as the stable 133Cs in various ores and to a lesser extent in soil. It occurs in useful amounts in some varieties of beryl, but pollucite, an aluminosilicate of cesium, is still the only rich source. Absorption of cesium from the stomach to blood is assumed to be negligible, the same as for potassium. On the contrary, fractional absorption from the small intestine appears to be nearly complete under most conditions but may be reduced substantially by the presence of certain substances in the contents. When cesium is ingested in the form of chloride (and, probably, other halides like bromide and iodide), the absorption represents nearly 100% Cesium is eliminated in humans primarily through the kidneys. The biokinetic model provides the following percentages: urine 85%, feces 13%, and sweat 2%.