In HCP, the [2D] Hexagonal packed layers are arranged in ABAB form. The same happens in Primitive Hexagonal Unit Cell. So does that mean they are the same? If not what differentiates one from the other?

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    – Zenix
    Commented May 23, 2020 at 8:20
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1 Answer 1


the same happens in primitive hexagonal unit cell

Herein lies the gap in your concept: The same does not happen in primitive hexagonal unit cell. Here's an image to clear things up

enter image description hereenter image description here

The left one is a primitive hexagonal unit cell whereas the right one is a HCP lattice. To use your terminology, a simple primitive cell has packing of the type AAAA.. whereas a HCP cell has packing of the type ABAB..

I highly recommend reading your textbook or referring to some more material on solid state chemistry, such as this SlideShare presentation on basic crystallography.

  • $\begingroup$ So from 2d hexagonal packed layers we can make 1) HCP and 2)CCP but not Primitive Hexagonal Unit Cell?? $\endgroup$ Commented May 23, 2020 at 12:56
  • $\begingroup$ Yes you can. How to do so is an exercise left for the reader. $\endgroup$ Commented May 23, 2020 at 13:00
  • $\begingroup$ the second part of the question, can Primitive Hexagonal Unit Cell be made in the same way by arranging the 2D hexagonal layers in AAA type?? $\endgroup$ Commented May 23, 2020 at 13:01
  • $\begingroup$ The answer to this last question of yours is already here on this page, a few lines above. $\endgroup$ Commented May 23, 2020 at 13:39
  • $\begingroup$ There is no such thing as an HCP lattice in terms of classifying symmetry. HCP is a primitive hexagonal structure with two atoms in the primitive cell (one per asymmetric unit). See chemistry.stackexchange.com/a/134572 $\endgroup$
    – Karsten
    Commented Jun 3, 2020 at 21:49

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