what does coordination no in crystal structures really mean? i know it's no of nearest neighbors but has it significantly to do with bonding of electrons. actually my doubt is that - I read Be can't show coordination no of 6 and is allowed to show only coordination no 4 due to lack of orbitals. Just few minutes ago i read that it is packed in HCP type of lattice "Beryllium is a steel gray and hard metal that is brittle at room temperature and has a close-packed hexagonal crystal structure." source wikipedia we know in HCP coordination no is 12 So in crystals what feeling of coordination no. must i get???