Crystalline, transparent (6)
I believe the answer is:
limpid
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">crystalline</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that crystalline can be written as limpid)</span><br/ ><br/ >'<span class="explanation-format__original">transparent</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that transparent can be written as limpid)</span><br/ ><br/ ></span>
(Other definitions for limpid that I've seen before include "Translucent" , "'Of liquid, clear and transparent (6)'" , "Crystal clear as water may be" , "Crystal clear like pure water" , "Crystal-clear" .)