The faces you can see on your gypsum crystal come from crystallisation speed anisotropy. You could determine the orientation of these faces with XR Laue diffraction experiment.

The XRD (pwd) pattern you get represent all the HKL planes of your structure accordind to the Bragg law, along with primary and secondary extinctions, and modulation of intensity due to atom position in the structure.

There is no direct relation, as far as I know, between morphological shape and intensity of a XR diffracted pic (if your pwd is not textured).

For fun, you could try to measure angles from faces and check by calculus between and ' faces if it is coherent, you'll find the formula in a crystallography text book.

Diffraction peaks are related to interplanar distance d of the HKL crystallographic planes by the Bragg equation. lambda = 2d sin(theta); lambda = wavelenght of the X-rays, theta = diffraction angle. Instead, there is no relationship between the morphological faces and diffraction peaks.