Plutonium is a rare transuranic radioactive element with the Atomic symbol Pu, and the Atomic number 94. It is an Actinide metal with a silvery-white appearance that tarnishes when exposed to air, much like Thorium. It will form a dull coating when oxidized. It reacts with carbon, halogens, nitrogen and silicon. When exposed to moist air, it forms oxides and hydrides that expand the sample up to 70% in volume. It is also a radioactive poison that accumulates in bone marrow. This makes the handling of plutonium dangerous.