Heat capacity studies of phase transitions in langbeinites II. K2Mg2(SO4)3

Heat capacity measurements have been made on a synthetic sample of langbeinite, K₂Mg₂(SO₄)₃, from 13 to 342 K in an adiabatic calorimeter. Three phase transitions, at 51.0, 54.9 and 63.8 K, have been observed in this material. Our study is the first to report the existence of such phase transitions in K₂Mg₂(S0₄)₃ and disputes predictions that none would take place below 77 K. Two models which have been proposed to explain the transition in potassium langbeinites are discussed in light of these results.