Rocky mineral broken by fine soldier (8)
I believe the answer is:
rifleman
'soldier' is the definition.
(I've seen this before)
'rocky mineral broken by fine' is the wordplay.
'rocky' is an anagram indicator.
'broken by' is an insertion indicator.
'fine' becomes 'f' (abbreviation).
'mineral' with letters rearranged gives 'rileman'.
'rileman' enclosing 'f' is 'RIFLEMAN'.
(Other definitions for rifleman that I've seen before include "British private soldier - New Zealand songbird" , "Bird" , "Armed soldier" , "Soldier - crack shot?" , "Soldier carrying gun" .)