Hard rock in grate crumbled (7)
I believe the answer is:
granite
'hard rock' is the definition.
(I've seen this before)
'in grate crumbled' is the wordplay.
'crumbled' indicates an anagram.
'in'+'grate'='ingrate'
'ingrate' with letters rearranged gives 'GRANITE'.
(Other definitions for granite that I've seen before include "Hard granular rock" , "A very hard rock from Tangier" , "Tangier (anag.)" , "Get rain (anag) - rock" , "Igneous rock, generally composed of feldspar and mica and quartz" .)