One might study rock music, finally departing from coolest gig around (9)
I believe the answer is:
geologist
'one might study rock' is the definition.
(geology is the study of rocks)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for geologist that I've seen before include "Specialist in the history of the earth in rocks" , "One studying the earth's crust" , "Specialist in the physical history of the earth" , "One studying rocks" , "One studying the earth's structure" .)