Granite rocks forming city (7)
I believe the answer is:
tangier
'city' is the definition.
(city in Morocco)
'granite rocks' is the wordplay.
'rocks' indicates an anagram.
'granite' is an anagram of 'TANGIER'.
'forming' acts as a link.
(Other definitions for tangier that I've seen before include "Moroccan seaport made of granite" , "Granite city just opposite Gibraltar" , "Seaport of Morocco, opposite Gibraltar" , "with more piquant flavour" , "Moroccan seaport opposite Gibraltar" .)