We perform a rigorous study of the identical sphere packing problem in Z 3 and of phase transitions in the corresponding hard-core model. The sphere diameter D > 0 and the fugacity u ≫ 1 are the varying parameters of the model. We solve the sphere packing problem for values D 2 = 2, 3, 4, 5, 6, 8, 9, 10, 12, 2ℓ 2 , ℓ ∈ N. For values D 2 = 2, 3, 5, 8, 9, 10, 12, 2ℓ 2 , ℓ ∈ N and u > u 0 (D) we establish the diagram of periodic pure phases, completely or partially.