Patina that's unusual in a snake (6)
I believe the answer is:
taipan
'a snake' is the definition.
(taipan is a kind of snake)
'patina that's unusual' is the wordplay.
'that's unusual' is an anagram indicator.
'patina' is an anagram of 'TAIPAN'.
'in' is the link.
(Other definitions for taipan that I've seen before include "Large brown, highly-venomous snake" , "Large Australian snake" .)