Stone in great pieces (7)
I believe the answer is:
granite
'stone' is the definition.
(granite is a kind of stone)
'in great pieces' is the wordplay.
'pieces' indicates an anagram (the same pieces in a new order).
'in'+'great'='ingreat'
'ingreat' anagrammed gives 'GRANITE'.
(Other definitions for granite that I've seen before include "Hard igneous rock" , "Showing great resolution" , "Very hard type of rock" , "Hard granular rock" , "Tearing (anag.)" .)