Redetermination of clinobaryl­ite, BaBe(2)Si(2)O(7)

Clinobaryl­ite, ideally BaBe(2)Si(2)O(7) (chemical name barium diberyllium disilicate), is a sorosilicate mineral and dimorphic with baryl­ite. It belongs to a group of compounds characterized by the general formula BaM (2+) (2)Si(2)O(7), with M (2+) = Be, Mg, Fe, Mn, Zn, Co, or Cu, among which the Be-, Fe-, and Cu-members have been found in nature. The crystal structure of clinobaryl­ite has been re-examined in this study based on single-crystal X-ray diffraction data collected from a natural sample from the type locality (Khibiny Massif, Kola Peninsula, Russia). The structure of clinobaryl­ite can be considered as a framework of BeO(4) and SiO(4) tetra­hedra, with one of the O atoms coordinated to two Be and one Si, one coordinated to two Si, and two O atoms coordinated to one Si and one Be atom. The BeO(4) tetra­hedra share corners, forming chains parallel to the c axis, which are inter­linked by the Si(2)O(7) units oriented parallel to the a axis. The Ba(2+) cations (site symmetry m..) are in the framework channels and are coordinated by eleven O atoms in form of an irregular polyhedron. The Si—O(br) (bridging O atom, at site symmetry m..) bond length, the Si—O(nbr) (non-bridging O atoms) bond lengths, and the Si—O—Si angle within the Si(2)O(7) unit are in marked contrast to the corresponding values determined in the previous study [Krivovichev et al. (2004 ▶). N. Jb. Miner. Mh. pp. 373–384].