Gemstone with a "fire" variety (4)
I believe the answer is:
opal
'gemstone with a fire variety' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for opal that I've seen before include "Birthstone for October" , "little jewel" , "Gem stone" , "Milky white gem" , "Semi-transparent gem" .)