Well EPR is the resonance absorption spectra for the system having unpaired electrons (ie. for systems where net spin is non zero). Rock samples do have many elements with unpaired electrons. I feel unless you quantify the elements in the rock sample, it is difficult to interpret. 

I think the same like previous answerer. Do the elemental analysis first: EDS, XRF anything what gives you what exactly is inside of your sample. Than if you have some specific ion or radical EPR spectra you can say something more about the rock. Probably high resolution EPR would be the best choice for you to gain a specific spectra and have hope that the rocks are not conductive.

Thanks dear colleges, I have already do DRX Analyses, for your information i told about source rock sample(shale) so what EPR can provide me again