Banded chalcedony (4)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">banded chalcedony</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 onyx that I've seen before include "Agate with alternating bands of colour" , "Form of chalcedony" , "Sort of agate" , "Gemstone, a variety of chalcedony" , "Stone-like marble with layered colours" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">banded chalcedony</span>' is the definition.<br/ >'<span class="explanation-format__answer">agate</span>' can be an answer for '<span class="explanation-format__original">chalcedony</span>' <span class="explanation-format__explanation">(agate is a kind of chalcedony)</span>. I also know that 'banded' relates to this answer.<br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for agate that I've seen before include "Quartz with bands of colour, used in jewellery" , "Variegated chalcedony" , "Quartz gem" , "Onyx" , "Semi-transparent stone" .)