Type of quartz (5)
I believe the answer is:
agate
'type of quartz' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for agate that I've seen before include "Quartz with bands of colour, used in jewellery" , "marble" , "Semi-precious quartz" , "Variegated chalcedony" , "On the way" .)