Sailor after degree in rock? (6)
I believe the answer is:
basalt
'rock?' is the definition.
(basalt is a kind of rock)
'sailor after degree' is the wordplay.
'sailor' becomes 'salt' (salt is a kind of sailor).
'after' says to put letters next to each other.
'degree' becomes 'BA' (Bachelor of Arts).
'salt' after 'ba' is 'BASALT'.
'in' is the link.
(Other definitions for basalt that I've seen before include "Type of rock is a blast, oddly" , "Black volcanic rock" , "Rock containing olivine" , "Dark rock of volcanic origin" , "Common volcanic rock" .)