I was revising solid state chapter when I came across this question
What is the maximum coordination number of an atom in a hcp crystal structure of an element?
The word 'maximum' drew my attention. The answer provided was 12, without any explanation.
Now, it is pretty easy to visualise that the coordination number of the two spheres in the middle of the top and bottom layer is 12, but what about the other ones?
After extending the lattice, it becomes clear that the coordination number of all spheres in layer A will be 12. The spheres in the original hexagon (layer A) can be seen as center points of some other hexagon.
Just confused about layer B.