There are also free software packages available like Fullprof or MAUD. Your major problem will be the clay minerals since they are quite tricky. The reason: usually they are no "classic" crystals anymore. Anisotropic lattice defects, the coherent volumes are small so that the diffraction signal is difficult to initerprete and introduced models are often only roughly applicable. Visit the following link. Every second year there is some kind of championship in phase fraction determination. 

http://www.clays.org/SOCIETY%20AWARDS/RCresults.html

thank you all for your reply...

In the link provided by Gert Nolze, it is also about input of Steve Hillier (author of a paper I provided you), who is among the best specialists in mineral quantification from Xray crystallographic data.Best regards.

Hello Bikash, how are you? I have this same problem... the one you asked 2 years ago, I think. Could you give me some advice, how to proceed. Thank you!

Carisa.

Hello Carisa... If u have the xpert high score plus software then first open the data file in the software...then go to treatment section and search peaks (u can do it by automatic mode or by selecting peaks manually) and click on accept. Then go to analysis section and go for search match....now before applying search go to restriction section...select the sub-file 'minerals'. if u know the probable mineralogy of the rock then in the restriction section select the possible elements in the periodic table. Now click on search tab. a set of possible minerals are appeared in the right tab of the screen. Now select the possible minerals and drop them in the upper pan and go for reitvield refinement for quantitative analysis.

Kindly note that this is the general process to get the quantitative values. For better results consult with some people who are frequently using this software (probably the chemistry or metallurgy student). they will guide u in a better way.

Thank you very much Bikash! I'll start with your recommendations. Have a nice weekend.