Stress in stone that cracks (7)
I believe the answer is:
tension
'stress' is the definition.
(I know that stress can be written as tension)
'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 "Strained state" , "Strained condition" , "Intones (anag) - stress" , "Nervous strain" , "The effect of force exerted in or on something" .)