A rotary rock bit is disclosed having bearing surfaces utilized therein which have extremely long wear resistant properties. The rock bit comprises a plurality of legs extending downwardly from a main bit body. A cone cutter is rotatively mounted on a journal formed on each leg. One or more of the interengaging bearing surfaces between the cone and the journal includes a layer of diamond material mounted on a substrate of carbide. In one embodiment, the bearing material forms the thrust button adjacent the spindle located at the end of the journal. In another embodiment, the bearing material is located on the interengaging axial faces of the journal and cone. In still another embodiment, the bearing material is a segmented cylindrical bearing located in a circumferential groove formed in the journal.