Handheld firework (8)
I believe the answer is:
sparkler
'handheld firework' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sparkler that I've seen before include "Eg, a diamond" , "Firework - precious stone" , "Bright gem" , "Possibly brilliant" , "Slow-burning firework and a diamond" .)