EMPLOYEE EXITED TRUCK POSITIONING HIMSELF ON THE GROUND NEAR A PENDANT MOUNTED CONTROL STATION FOR AN ELECTRICALLY OPERATED GATE WHICH PERMITS LOADING OF COAL COARSE REFUSE FROM A 175 TON STORAGE BIN. AS EMPLOYEE OBSERVED LOADING OPERATION, A SMALL PARTICLE OF ROCK BOUNCED OFF THE TRUCK STRIKING HIM IN THE RIGHT EYE CAUSING AN ABRASION. WAS NOT WEARING SAFETY GLASSES.