Crystalline structure (7)
I believe the answer is:
lattice
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">crystalline structure</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 lattice that I've seen before include "Network of Wooden strips" , "Regular atomic structure" , "Ornamental framework" , "grill" , "Tactile (anag) - grille" .)