Partheite is a zeolite-like mineral of composition Ca2AI4Si401s(OH)2 . 4H20. It crystallizes with monoclinic symmetry, space group C2jc, a=21.555(3), b=8.761(1), c=9.304(2) A, p=91.55(2), Z=4, Dm=2.39 gjcm3, Dx=2.41 gjcm3. Its structure consists of T-centered T04 tetrahedra (T=AI,Si) which are connected via corners to a 3-dimensional framework. Due to the presence of hydroxyl groups the framewo...

The influence of the cations on the condensation of the anions in the salts (A')Zn(II) Br4 and (A)2Zn(II)Br4 is studied by 81 Br NQR and X-ray crystal structure analysis. (A')Zn(II)Br4(A' = [H3N(CH2)3NH3] + ) (1) shows a phase transition at 474 K. The phase II of (1) crystallizes with isolated [ZnBrJ " tetrahedra: monoclinic P2 t/«, Z = 4, a = 1108.4 (5), b = 1096.8 (2), c = 1118.5 (6) pm, and ...

By defining a closure operator on effective equivalence relations in a regular category C, it is possible to establish a bijective correspondence between these closure operators and the regular epireflective subcategories of C, on the model of the closure operators on kernels in homological categories [5]. When C is an exact Goursat category [6], this correspondence restricts to a bijection bet...