Abstract: The crystal structure of sophiite, Zn₂(SeO₃)Cl₂ (a = 10.251(4), b = 15.223(2), c = 7.666(5) Å, Z = 8) was solved in space group Pccn from single crystal X-ray data, and refined to R = 0.053 for 666 F_o > 4σ_Fo. The mineral belongs to layer compounds. The threefold coordinated Se atom is at the apex of a pyramid, the base of which is formed by three O atoms; Se-O = 1.69 Å. Zn cations occupy two positions with distorted tetrahedral and octahedral coordinations. In the tetrahedra, Zn cations are surrounded by two O (2.02 Å) and two Cl (2.224 Å) atoms. Zn octahedra contain four O atoms (2.07 Å) and two Cl atoms (2.701 Å). The atomic arrangement is characterized by rings containing two Se pyramids linked by their corners to two Zn tetrahedra. The rings are linked by their edges and corners to Zn octahedra to form layers parallel to (010). The layers are interconnected by residual Van der Waals bonds.

Experimental results on thermal phase transformations and deformations, crystal optics and other physical properties of sophiite are presented. A structural aspect of their anisotropy is discussed.