The Crystal Structure of Latiumite, a New Type of Sheet Silicate

The crystal structure of lat iumite, Kor.Ca"(Si"rrA1r..)O,,(SO,)or(COr)n sl a = 12.06, b- 5.08, c- 10.81 A, B = 106";space group P2r, Z- 2, has been determined on an Albano specimen, using Weissenberg data. The isotropic least-squares refinement led to a final R-index of 0.08. The main structural feature is the presence of double layers of (Si,Al) tetrahedra; the double layers, paral lel to the cleavage plane (100), are connected to each other by Ca-atoms and SO"- groups. The Si and Al atoms are ordered among the five symmetry independent tetrahedra. A pseudo-gl ide plane results in frequent twinning on (100)