In rock, various notes are used (5)
I believe the answer is:
stone
'in rock' is the definition.
'stone' can be an answer for 'rock' (I've seen this before). I'm not certain of the 'in' bit.
'various notes are used' is the wordplay.
'notes' can be anagrammed to 'STONE'.
However, I am not clear how this is indicated.
Can you help me to learn more?
(Other definitions for stone that I've seen before include "See 5" , "Piece of rock - weight" , "diamond, say" , "Kernel" , "Beryl, ruby" .)