That depends on your specific XRD set-up. Are you using a newer system with a computer integrated detector and analysis software package (such as X'PERT Quantify), or are you using a Debye-Scherrer Camera and developing your own film strip?
Assuming that you have the more modern set-up, it is relatively easy to search your scan for known peaks, although it will vary depending on your analytical software package. Generally you begin by removing your background, as well as K[tex]\alpha[/tex]2 radiation. You then may apply some line smoothing functions, depending on your scan rate, dwell time, and quality of diffraction pattern. You normally then select the elements that you expect to be present within the sample, and search for correlating peaks. If this does not work, you can usually tell the program exactly where your peaks are located using markers, then searching for peaks that correlate with your markers. Usually multiple patterns will match one or more of your peaks, so you then browse through the list of possible matches, and select the best fit (some shift in intensity and/or 2Theta angle may be required due to sample prep).
If you are using the film method, then you'll need a light table, and you'll have to measure the spacing of the resultant diffraction cones. You then select the three with the highest intensity, and calculate the planar spacings. You can then look up these spacings in an index of inorganic phases, and ensure an acceptable correlation. This process is long, and can be tedious, so hopefully you have a software package, but if not it can be done.
I hope this helps, as this is my first post on this site as I just found it today.
Dave,