Weight unit for gems (5)
I believe the answer is:
carat
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">weight unit for gems</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for carat that I've seen before include "A unit of weight for precious stones" , "Measure for diamonds or gold" , "Jewellery unit" , "Unit of weight for gems or purity of gold" , "Unit of weight for diamonds" .)