Beauty clasping trimmed gemstone trinket (9)
I believe the answer is:
bagatelle
'trinket' is the definition.
(I have seen 'lovely trinket' mean 'bagatelle' so perhaps 'trinket' could also mean 'bagatelle')
'beauty clasping trimmed gemstone' is the wordplay.
I cannot really see how this works, but
'gemstone' could be 'agate' (agate is a kind of gemstone) and 'agate' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for bagatelle that I've seen before include "Pinball game - something of little value" , "lovely trinket" , "Trivial matter" , "shooting game" , "Game; piece of music" .)