(above) cadmium atoms arranged in a hexagonal close packed pattern
Cadmium: metal whose atoms are arranged in closely packed hexagonal layers. First and third layers are in line with each other. This gives what is known as a hexagonal close packing. However, in cadmium, the Cd-Cd bonds are of two different lengths, making the hcp unit cell relatively taller than an ideal hcp. Consequently, the cadmium atoms are drawn as ovoids.
Image is 500 pixels across, the originals are 4096 pixels across.