Fine quality diamonds worn on shirt in New York (6)
I believe the answer is:
nicety
'fine quality' is the definition.
'nicety' can be an answer for 'quality' (thesaurus). I'm unsure of the 'fine' bit.
'diamonds worn on shirt in new york' is the wordplay.
'diamonds' becomes 'ice' (slang term for diamonds).
'worn on shirt' becomes 't' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'new york' becomes 'ny'.
'ice'+'t'='icet'
'icet' inserted within 'ny' is 'NICETY'.
Can you help me to learn more?
(Other definitions for nicety that I've seen before include "Refinement" , "A detail of etiquette" , "Judged to a . . . . . . - with precision" , "Exactitude" , "Delicacy" .)