Banded mineral (5)
I believe the answer is:
agate
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">banded mineral</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for agate that I've seen before include "Variety of chalcedony" , "Semi-precious quartz" , "Banded ornamental stone" , "Quartz variety" , "Variegated chalcedony" .)