It happens to be the one with the smallest angle which I measured as 23.04 degrees. This is another peak picked for no special reason. This corresponds to a d-spacing of 2.287 angstrom. E. This is the largest peak on the pattern. It actually extends several times the height of this image.
Many factors affect the intensity of a given peak.
You can see a partial list of calcite peaks. The 'Mineral of the Month challenges you to use Bragg's Law and a diffraction pattern to identify a mineral. We can measure 2-theta from the diffraction pattern. Divided by 2, these values become theta. This is a very brief treatment of a large and interesting subject.