Using a system of first nearest neighbour bonds it is shown that upon applying the PBC theory of Hartman and Perdok to garnet, ten F slices are obtained. These result from combinations of 47 PBCs. Upon applying rigorous rules, obtained among others from a statistical mechanical tetrahedron model, the ten F slices are simplified. The relative morphological importance of faces is predicted using the sum and product of edge energies as criteria and it is shown that good agreement between predicted and observed kinetic and morphological data of both synthetic and natural garnets is obtained. The occurrence of interlaced spirals is explained. © 1983.