Antimony
Antimony has four allotropes. The common allotrope of antimony is a blue-white metalloid. It looks black when powdered. It is brittle, soft, and shiny. Yellow and black antimony are unstable nonmetals. Yellow antimony is only found at very cold temperatures. It is made by oxidation of stibine. It turns into black antimony when light is shined on it or when it is warmer. Black antimony is normally made by heating metallic antimony until it boils and then cooling the vapors very quickly. It can ignite spontaneously (without any ignition source like a spark or a flame). It also corrodes easily. There is another explosive form of antimony that is made by electrolysis of antimony trichloride. This antimony explodes when changing into the metallic form. There is no chemical reaction; the atoms in the antimony crystal are rearranging themselves. When antimony is talked about it normally means the blue-white metalloid form, since it is most common.