Surface of a cut gemstone (5)
I believe the answer is:
facet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">surface of a cut gemstone</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for facet that I've seen before include "Side of a cut gem" , "view" , "Aspect or feature of something" , "Look" , "Small flat surface of cut gemstone" .)