Chalcedony variety (5)
I believe the answer is:
agate
'chalcedony variety' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for agate that I've seen before include "Onyx" , "Quartz with bands of colour, used in jewellery" , "rock with bands" , "marble" , "Semi-transparent stone" .)