A NEW ANTHROPOGENIC (K, NH4) MGCL3-CENTER-DOT-6H(2)O PHASE AT THE LOCATION BUNTE-FIRST IN THE REPOSITORY FOR RADIOACTIVE-WASTES IN MORSLEBEN, GERMANY

A previously unknown phase of potassium ammonium magnesium chloride he xahydrate was found at the location ''Bunte First'' in the salt mine ' 'Marie'' in Morsleben; the mine is used as a repository for low-level radioactive wastes. Conditions of crystal growth were investigated. Th e substance, with composition K-0.64(NH-(4))(0.36)MgCl3 . 6H(2)O, is m onoclinic with lattice constants a = 6.66(2), b = 6.68(1), c = 13.22(4 )Angstrom, beta similar to 90 degrees and Z = 2. The very pressure sen sitive crystals are always multiple twins according to (001). The X-ra y diffraction pattern contains satellite reflections in the a-directi on. Due to the extinctions of main reflections, the average structure can be assigned to the space group Pc or P2/c. The structure is closel y related to the NH4MgCl3 . 6H(2)O-structure (the b-axis in the new ph ase corresponds approximately to [110]/2 in the ammonium magnesium chl oride hexahydrate structure).