Unusual setting for garnets (7)
I believe the answer is:
strange
'unusual' is the definition.
(I know that unusual can be written as strange)
'setting for garnets' is the wordplay.
'setting for' indicates anagramming the letters (letters set or arranged differently).
'garnets' is an anagram of 'STRANGE'.
(Other definitions for strange that I've seen before include "Irregular" , "Odd kind of garnets" , "Weird, eerie" , "Odd, peculiar" , "Abnormal" .)