Four langbeinite [K2Mg2(SO4)3> single grains from the Stebnyk evaporite mine have been dated with the laser step-heating 40Ar/39Ar method. These yield very clustered ages, including a high quality plateau age of 14.31 ¿ 0.06 Ma for 99.5% 39ArK released. These Middle Miocene ages disagree with the inferred Early Miocene age of the Stebnyk deposit [Peryt and Kovalevich, 1997>. Therefore, langbeinite may be formed after primary evaporite deposition in a maximum time interval around 7.5 Ma, during a diagenetic process or as a result of a fluid circulation. However the stratigraphic age may have been also overestimated due to a complicated tectonic history and the absence of clear stratigraphic markers. This work confirms the suitability of langbeinite for 40Ar/39Ar dating. Langbeinite in evaporites may thus be used for stratigraphic dating when primary, or for dating diagenesis or fluid circulation when secondary. ¿ 2001 American Geophysical Union