I perform wearing jaunty gemstone (7)
I believe the answer is:
peridot
'gemstone' is the definition.
(I know that peridot is a type of transparent gem)
'i perform wearing jaunty' is the wordplay.
'perform' becomes 'do' (both can mean complete an action).
'wearing' means one lot of letters goes inside another.
'jaunty' becomes 'pert' (I've seen this before).
'i'+'do'='ido'
'ido' put within 'pert' is 'PERIDOT'.
(Other definitions for peridot that I've seen before include "olivine" , "I deport (anag) - gemstone" , "Gem" , "A green semi-precious stone" , "Pale green gemstone" .)