Uranium

Uranium (U) is very dense, heavy and silvery-white metal, found naturally as ore in deposits. It is composed of three major isotopes, uranium 238 (more than 99%), uranium 235 (0.72%), and uranium 234 (0.005%).
Exposure to uranium can result in both chemical and radiological toxic effects. Chemical toxicity: Uranium is very toxic after ingestion or inhalation, main target organ is the kidney.
See also: uranium 235, uranium 238