The Collaborative International Dictionary of English v.0.48:

Sea coal \Sea" coal`\
   Coal brought by sea; -- a name by which mineral coal was
   formerly designated in the south of England, in distinction
   from charcoal, which was brought by land.
   [1913 Webster]

   Sea-coal facing (Founding), facing consisting of pulverized
      bituminous coal.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sea coal
    n 1: pulverized bituminous coal; used as a foundry facing