Constructing and positioning a second close packed layer. (a) and (b). A red sphere in a second layer nestles in the dip created between three blue spheres in the first layer.
(c) A second red sphere in the second layer can only be placed in the dips marked ○ ; there is insufficient room to place the second sphere in the dips marked × .
(d) placing more red spheres in the second layer builds up a second close-packed layer (red spheres) slightly-shifted positionally from the first close- packed layer (blue spheres).