Some rock that's unfashionable: member of The Police covering Queen (7)
I believe the answer is:
outcrop
'some rock' is the definition.
(outcrop is a kind of rock)
'unfashionable member of the police covering queen' is the wordplay.
'unfashionable' becomes 'out' (synonyms).
'member of the police' becomes 'cop' (I am not sure about this - if you are sure you should believe this answer much more).
'covering' indicates putting letters inside.
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'cop' placed around 'r' is 'crop'.
'out'+'crop'='OUTCROP'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for outcrop that I've seen before include "Part of a rock formation above the surface" , "Rocks projecting from ground" , "Jutting stone" , "Protruding or projecting rock" , "Cop tour around projecting layer of rock" .)