In order to properly understand this I would recommend that you read a good introductory textbook on crystallography and X-ray diffraction. In short different planes (with different Miller indices) exist in the crystal structure of each mineral. Each of these planes have their own d-spacing. Depending on the space group of the mineral in question certain planes will refract and give reflections in the XRD pattern. So the fact that you get reflections at 1.181 and 3.344 angstrom is due to the fact that different planes are refracting.

yes right sir Theo Kloprogge 

thanks for your precious comments