The Columbia Encyclopedia, Sixth Edition. Columbia Encyclopedia World Factbook Columbia Gazetteer American Heritage Coll.
Radium is a lustrous white radioactive metal.
When it is exposed to air, a black coating of nitride rapidly forms. It combines directly with water to form the hydroxide. It reacts with acids to form the commercially important chloride and bromide. Mixed with a phosphor such as zinc sulfide, radium compounds are used in luminous paints. Radium is a rare metal.