FRICTIONAL IGNITION OCCURRED ON THE NORTH 004 SECTION APPROX 90' IN THE #9 ENTRY BETWEEN BLOCK 37 & 38. OPERATOR SAW AN ORANGE BALL THAT STARTED APPROX IN THE CENTER OF THE CUTTER HEAD & SPREAD TO THE RT END. BALL LASTED APPROX 3 SECONDS. THERE WAS NO POP JUST SOME SMOKE. NO CHARRING WAS FOUND & THE INVESTIGATION DETERMINED THAT BITS STRIKING THE SANDSTONE CAUSED THE INCIDENT.