Hexagonal close packing (hcp): 1)In hcp , the spheres of the third layer are exactly aligned with those of the first layer. 2)This arrangement is represented as AB AB....type. 3)In this arrangement, the tetrahedral voids of the second layer may be covered by the spheres of the third layer. Cubic close packing (ccp): 1)In ccp,the spheres of the third layer are not aligned with those of the first layer or second layer. 2)This arrangement is represented as ABC ABC ....type. 3)In this arrangement, the third layer may be placed above the second layer in a manner such that its spheres cover the octahedral voids.