This was a movie that I saw a portion of back in the mid 80's on either HBO - The movie channel or Cinemax . There were two (English guys)...I think they were English, anyway. There was a black-stone with a white (marking or swirl) upon it. And if the stone was struck/hit one of the men could feel it somehow and would wail in agony. Even though I'm fairly sure that the film was called the stone; I have never even come close to finding anything similar.