Ornamental stone, a variety of chalcedony (5)
I believe the answer is:
agate
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">ornamental stone</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">a variety of chalcedony</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for agate that I've seen before include "Stone with coloured bands" , "Variety of chalcedony" , "Impure form of quartz with banded chalcedony, used as a gemstone" , "rock with bands" , "Quartz variety" .)