Tanitia said that the Rabid Togs compulsively stole shiny things, so if there were Petralith fragments in the Humnaz territory the Togs would probably have bits and pieces. Surprisingly, she was absolutely right. When you killed Rabid Togs, many of them had Petralith Fragments. You brought them to a pleased Tanitia, who rewarded you, but then realised that the fragments were fakes.