Silicate mineral (4)
I believe the answer is:
mica
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">silicate mineral</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 mica that I've seen before include "Isinglass" , "Transparent mineral" , "Flexible mineral found in igneous and metamorphic rocks" , "Shiny silicate mineral" , "Semitransparent insulating mineral" .)