Abstract Amicite from Howenegg (Germany), schematic formula K 4 Na 4 Al 8 Si 8 O 32 ·10H 2 O, space group I 2, dehydrated in vacuum for 56 h [amicite (56 h)] and 6 days [amicite (6 d)], transforms into two new phases. In amicite (56 h) approximately 2/3 of the water molecules have been removed, and a strong decrease in the cell volume (11.3%) occurs. The framework is strongly distorted, and the channels are squashed. A rearrangement of extra-framework species causes a change in the space group to P 2 1 . Amicite (6 d) is completely dehydrated, whereas the framework does not undergo a further deformation with respect to the (56 h) sample. The original symmetry is restored, and Na and K atoms are both split over two half-occupied sites. The dehydration behavior of amicite differs from that of other members of the gismondine family, gismondine and garronite, mainly because these two do not completely dehydrate before the destruction of the structure. This fact is interpreted as due to the presence of monovalent cations in amicite, whereas Ca is present in gismondine and garronite.