Natural magnet
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">natural magnet</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lodestone that I've seen before include "Naturally magnetic rock" , "Natural magnetic ore" , "Magnet" , "Piece of magnetic iron ore" , "Mineral" .)