Transparent mineral (7)
I believe the answer is:
crystal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">transparent mineral</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 crystal that I've seen before include "The fortune teller may use a . . . . . . . ball" , "Type of clear-cut, lucent glass" , "Glass made at Waterford" , "Regular-shaped mineral piece" , "Highly transparent glass" .)