Rock singer initially with Mick? (9)
I believe the answer is:
sandstone
'rock' is the definition.
(sandstone is a kind of rock)
'singer initially with mick?' is the wordplay.
'initially' indicates taking the first letters.
'with' becomes 'and'.
'mick?' becomes 'stone' (I can't explain this - if you can you should give a lot more credence to this answer).
The initial letter of 'singer' is 's'.
's'+'and'+'stone'='SANDSTONE'
Can you help me to learn more?
(Other definitions for sandstone that I've seen before include "Such building material" , "Rock containing quartz grains" , "Type of sedimentary rock" , "Among the best of building materials" .)