Mollusk-shell material
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mollusk-shell material</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 nacre that I've seen before include "Pearl's mum" , "inside of shell" , "Mother-of-pearl from shellfish" , "Constituent of inlay furniture" , "valuable material" .)