Michael,
  It -does- look like coal.  I'm trying to figure out how the car would have gotten that
wide a 'dusting' of coal ... And - that high up on the sides and up onto the roof.
  Wasn't bulk coal loaded using a chute stuck into the car after the open door had
been closed up enough to set the level (weight) of the load?  Does coal being
run thru a chute produce that much dust?  How does bulk coal produce such 
well defined 'limits' outside of the doorway?  That car looks like someone used
an airbrush to simulate the weathering!  *G*
                                                                                                 - Jim B.