Radium is an almost pure-white alkaline earth metal, but it readily reacts with nitrogen (rather than oxygen) on exposure to air, forming a black surface layer of radium nitride (Ra3N2).
Radium murni mawarna putih masawang pérak, menawi aluh maréaksi sareng nitrogén (nénten oksigén) ri kala kena udara, ngawentuk lapisan pamukaan ireng radium nitrida (Ra3N2).