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