Kind of rock music essentially gone weird (7)
I believe the answer is:
igneous
'kind of rock' is the definition.
'music essentially gone weird' is the wordplay.
'essentially' indicates the central letters.
'weird' indicates anagramming the letters.
The middle letters of 'music' are 'usi'.
'usi'+'gone'='usigone'
'usigone' is an anagram of 'IGNEOUS'.
(Other definitions for igneous that I've seen before include "Originally molten (rock)" , "Like fire - type of rock" , "Type of rock with molten origin" , "(Of rocks) formed from lava or magma" , "Maybe fiery" .)