1976 Volume 8 Issue 3 Pages 184-192
Crystal structure of sugilite has been refined by the least squares method using 435 reflections measured on an automated single crystal diffractometer using MoKα radiation. The final unweighted R-factor is 0.047 for 429 reflections. The cell dimensions are: a=10.007(2), c=14.000(2)Å; space group P6⁄mcc. Sugilite is isostructural with milarite group minerals, and can be described as (K0.81Na0.19) (H2O0.91Na0.64)2 (Fe3+1.32Na0.59Ti4+0.06Fe2+0.03)2 (Li2.12Al0.59Fe3+0.29)3Si12O30 with Z=2 by structure formula of milarite group defined by Forbes, Baur and Khan (1972). The SiO4 tetrahedra from hexagonal double rings with the composition Si12O30. These double rings are linked by Li, Al and Fe3+ atoms in tetrahedral four-coordination to form a tetrahedral frame structure. Na and H2O are located in nine-coordinated sites.