"Mother of mine" could be an affectionate term. Kind of like "mother dearest." I don't think it's really common, though. It seems antiquated.

'My mother' is the term you use when you are talking to another person ABOUT your mother. You refer to her as 'my mother' . Grammatically this is a noun phrase in the third person, like he or she, ie My mother is a teacher 'Mother of mine' is a very old-fashioned term of address that people used to use when they were talking TO their mothers. Grammatically this is in the second person (vocative case) ie you. eg 'Mother of mine, you are so kind' You might come across it in an old text or song, but it is not used seriously nowadays. My kids would only call me that to be funny. Obviously these days, people say 'Mum' or 'Mom' to their mothers. I hope that's clear.

Thank you!!:)

My mother is usual whereas mother of mine is unusual.