Crossword Genius

Half of that rift zone is rocky, non-functional (2,3,5)

Ross

I believe the answer is:

on the fritz

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'non-functional' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'half of that rift zone is rocky' is the wordplay.
'half of' means to take half the letters.
'is rocky' is an anagram indicator (letters rocked or thrown around).
'that' cut in half is 'th'.
'th'+'rift'+'zone'='thriftzone'
'thriftzone' is an anagram of 'ON THE FRITZ'.

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I've seen this clue in The Independent.
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