In a kind of miracle, they say you are fickle (9)

I believe the answer is:

mercurial

'are fickle' is the definition.
(thesaurus)

I don't understand the rest of the clue.

(Other definitions for mercurial that I've seen before include "lively" , "Volatile" , "Temperamental" , "Changing unpredictably" , "Changeable in mood" .)

I've seen this clue in The Guardian.

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