Purple stone (8)
I believe the answer is:
amethyst
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">purple stone</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 amethyst that I've seen before include "One showing sparkling facets" , "February stone" , "rock" , "Purplish gemstone" , "Violet-coloured stone" .)