6

8

10

12

(A) and (B)

(C) and (D)

(A) and (C)

(B) and (D)

hcp and bcc

hcp and ccp

bcc and ccp

bcc and simple cubic cell

74

68

32

26

The coordination number is 12.

It has 74% packing efficiency.

Tetrahedral voids of the second layer are covered by the spheres of the third layer.

In this arrangement spheres of the fourth layer are exactly aligned with those of the first layer.