The crystal structure of tuscanite Available to Purchase

The crystal structure of tuscanite [K_0.88Sr_0.04(H₂O)_1.08](Ca_5.25Na_0.51Fe_0.10⁺³ Mg_0.11)(Si_6.34Al_3.66)O₂₂(SO₄)_l.38(CO₃OH)_0.55(O₄Н₄)_0.11] space group P2₁/a,a = 24.03(2), b = 5.11(1), с = 10.88(2) A, β = 106.94(9)°, was determined by direct methods using diffractometric data. Anisotropic thermal refinement led to a final R value of 0.034 (R_w = 0.038). The crystal structure is characterized by the presence of double layers of (Si,Al) tetrahedra; the double layer can be described, as in latiumite, as made up by five-membered rings, nearly parallel to (010), but whereas in latiumite each tetrahedron in the ring points upward, in tuscanite three tetrahedra in every ring point upward and two downward. These layers are connected by calcium and sulphate ions, as in latiumite; whereas in latiumite successive layers are related by unit translation, in tuscanite they are related by a glide plane. The substitutions of (CO₃OH) and (H₄O₄) for SO₄ are proposed and discussed.