October gems (5)
I believe the answer is:
opals
'october gems' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for opals that I've seen before include "jewellery" , "Milky sparkling gemstones" , "Precious stones" , "Milky gemstones with delicate colours" , "Iridescent gems" .)