The crystal structure of beryllonite from the type locality and comparison with isopointal structures

The crystal structure of beryllonite, NaBePO4, has been re-evaluated based on high-resolution X-ray diffraction data using a single crystal from the type locality, Stoneham (Maine, USA). Beryllonite is monoclinic, with a = 8.1309(2) Å, b = 7.7974(2) Å, c = 14.1918(4) Å, ß = 90.039(1)°, V = 899.76(4) Å3, space group P21/n (no. 14), Z = 12. Full anisotropic crystal-structure refinement converged to an R1 value of 0.0504 based on all 9435 unique reflections in the θ range 2–50°. The crystal structure consists of a framework of PO4 and BeO4 tetrahedra sharing all vertexes with adjacent tetrahedra. On the (010) plane, each tetrahedron shares three vertexes with three different tetrahedra forming a quasi-ditrigonal 63 net with alternating PO4 and BeO4 tetrahedra. The remaining vertex of each PO4 and BeO4 tetrahedra points outside the (010) plane and allows corner-linkage among the tetrahedral sheets. Na-centred polyhedra with six-and nine-fold coordinations are located in channels defined by the framework of tetrahedral rings. Beryllonite is isostructural with several natural and synthetic compounds and for these, a quantitative comparison of the crystal-chemical features is reported