The refined lattice parameters of beryllonite are:a=8.178 (3) A,b=7.818 (2) A,c=14.114 (6) A, β=90.00° (2); space groupP21/n,Z=12. Integrated Weissenberg photographs were taken by using CuK α radiation and multiple film packs. The anisotropic refinement of the crystal structure by means of least-square methods gave a finalR value of 0.063 for the 1388 observed reflections. In the crystal structure PO4 and BeO4 tetrahedra, linked by shared oxygen atoms in a three-dimensional network, form pseudo-ditrigonal rings perpendicular to theb axis. The independent Na atoms lying in the channels formed by the rings are coordinated as an irregular “nine-cornered” polyhedron and as distorted octahedra.