Ring with inset rare gem (5)
I believe the answer is:
pearl
'gem' is the definition.
(I know that pearl is a type of gem)
'ring with inset rare' is the wordplay.
I cannot really understand how this works, but
'rare' could be 'r' (listed by Oxford Dictionary of Abbreviations) and 'r' is found in the answer.
'ring' could be 'peal' (synonyms) and 'peal' is located in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for pearl that I've seen before include "greatly valued" , "Smooth lustrous round structure of calcium carbonate" , "Oyster growth" , "Precious gem" , "Much loved and valued person" .)