Pressure in stone that cracks (7)
I believe the answer is:
tension
'pressure' is the definition.
(pressure can mean tension or stress)
'in stone that cracks' is the wordplay.
'that cracks' is an anagram indicator (I've seen 'cracked' mean this).
'in'+'stone'='instone'
'instone' with letters rearranged gives 'TENSION'.
(Other definitions for tension that I've seen before include "Assay" , "Anxiety" , "Strained condition" , "Stretched state" , "State of strain or suspense" .)