Brown coal (7)
I believe the answer is:
lignite
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">brown coal</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for lignite that I've seen before include "it'll burn" , "Fuel" , "Brown coal" , "Soft brownish coal" , "rock" .)