Gemstone, part of robbery loot (5)
I believe the answer is:
beryl
'gemstone' is the definition.
(beryl is a kind of gemstone)
'part of robbery loot' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'BERYL' is hidden in the letters of 'robbery loot'.
(Other definitions for beryl that I've seen before include "Girl's name; gem" , "Pale greenish" , "Girl" , "Girl's name - precious stone" , "- Bainbridge, English novelist" .)