Chalcedony (5)
I believe the answer is:
agate
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">chalcedony</span>' is the definition.<br/ ><span class="explanation-format__explanation">(agate is a kind of chalcedony)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for agate that I've seen before include "Semi-transparent stone" , "Quartz with bands of colour, used in jewellery" , "Banded ornamental stone" , "Hard stone with concentric bands of colour" , "Impure form of quartz with banded chalcedony, used as a gemstone" .)