Needs tool to break rock (9)
I believe the answer is:
lodestone
'rock' is the definition.
'needs tool to break' is the wordplay.
'to break' indicates anagramming the letters.
'needs'+'tool'='needstool'
'needstool' with letters rearranged gives 'LODESTONE'.
(Other definitions for lodestone that I've seen before include "Magnetite" , "Magnet" , "Natural magnetic ore" , "naturally attractive?" , "attractive person" .)