Stone Sour quiet, for a change (9)
I believe the answer is:
turquoise
'stone' is the definition.
(I have seen 'Precious stone ' mean 'turquoise' so perhaps 'stone' could also mean 'turquoise')
'sour quiet for a change' is the wordplay.
'for a change' indicates anagramming the letters.
'sour'+'quiet'='sourquiet'
'sourquiet' anagrammed gives 'TURQUOISE'.
(Other definitions for turquoise that I've seen before include "Bluey-green" , "Greenish-blue gem" , "not quite green" , "Aquamarine colour" , "Sort of blue" .)