Violet gem (8)
I believe the answer is:
amethyst
'violet gem' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for amethyst that I've seen before include "One showing sparkling facets" , "Purplish gemstone" , "Precious stone of purple quartz" , "Violet gemstone" , "Semiprecious stone of violet or purple quartz" .)