In store, no rocks: just this one? (9)
I believe the answer is:
ironstone
'just this one?' is the definition.
The definition suggests a singular noun which matches the answer.
'in store no rocks' is the wordplay.
'rocks' is an anagram indicator.
'in'+'store'+'no'='instoreno'
'instoreno' is an anagram of 'IRONSTONE'.
(Other definitions for ironstone that I've seen before include "Material" , "Pottery" , "Earthenware" , "Sort of rock" , "Mineral" .)