Formal separation of one church into two (6)
I believe the answer is:
schism
'formal separation of one church into two' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for schism that I've seen before include "Breach within a church organisation" , "break" , "Splinter group" , "Church disunity" , "Breach or split in a church" .)