Cadmium Iodide structure

Cadmium iodide (CdI₂) has a hcp arrangement of iodide ions, with cadmium inside the octahedral holes of every other layer (so half the octahedral holes). It is often shown as sheets:

Here is the unit cell:

While you can just repeat the unit cell if you need the structure, the picture below will allow you to memorise it more directly:

Since the structure is composed of sheets, the patten repeats both parallel to and in towards the screen.