▪ Rastsvetaeva, R.K., Aksenov, S.M., Verin, I.A. (2012): Crystal structure of the NaCa(Fe2+,Al,Mn)5[Si8O19(OH)](OH)7·5H2O mineral: A new representative of the palygorskite group. Crystallography Reports, 57, 43-48.
A specimen of a new representative of the palygorskite–sepiolite family from Aris phonolite (Namibia) is studied by single-crystal X-ray diffraction. The parameters of the triclinic (pseudomonoclinic) unit cell are as follows: a = 5.2527(2) Å, b = 17.901(1) Å, c = 13.727(1) Å, alpha = 90.018(3), beta = 97.278(4), and gamma = 89.952(3). The structure is solved by the direct methods in space group P-1 and refined to R = 5.5% for 4168 F > 7(F) with consideration for twinning by the plane perpendicular to y (the ratio of the twin components is 0.52 : 0.48). The crystal chemical formula (Z = 1) is (Na1.6K0.2Ca0.2)[Ca2(FeAl1.6Mn0.8)(OH)9(H2O)2][(FeTi0.1)(OH)5(H2O)2][Si16O38(OH)2]·6H2O, where the compositions of two ribbons of octahedra and a layer of Si tetrahedra are enclosed in brackets. A number of specific chemical, symmetrical, and structural features distinguish this mineral from other minerals of this family, in particular, from tuperssuatsiaite and kalifersite, which are iron-containing representatives with close unit cell parameters.
Edited 1 time(s). Last edit at 02/01/2012 10:52AM by Marco E. Ciriotti.