Thorium (7440-29-1)

    Thorium (CAS NO.7440-29-1) is slowly attacked by water, but does not dissolve readily in most common acids, except hydrochloric. It dissolves in concentrated nitric acid containing a small amount of catalytic fluoride ion.Thorium is dimorphic, changing at 1400 °C from a face-centered cubic to a body-centered cubic structure. 
    Pure thorium is a silvery-white metal which is air-stable and can retains its luster for several months. Pure thorium is soft, very ductile, and can be cold-rolled, swaged, and drawn,and  often contain several tenths of a percent of the oxide. 
    Powdered thorium metal is often pyrophoric and should be carefully handled. When heated in air, thorium metal turnings ignite and burn brilliantly with a white light. Thorium has the largest liquid range of any element: 2946 °C between the melting point and boiling point.
    If thorium is contaminated with the oxide, it will  slowly tarnishes in air, becoming gray and finally black.

Reported in EPA TSCA Inventory.