Correct: it is a "brockage", and it is indeed a mint error. It happens when a coin gets stuck onto one of the dies. The coin then "becomes the die" for the next coin that is struck, creating a mirror-image-incuse version of the design of the opposite die.
I'm assuming, given your reported weight, that it is a threepence or at least threepence-sized. Unfortunately, as such it cannot be unequivocally confirmed to be a New Zealand coin, since Rhodesia & Nyasaland used this exact same obverse on its threepences. I'm not sure how common brockages are in either the New Zealand or Rhodesian series.
I'm assuming, given your reported weight, that it is a threepence or at least threepence-sized. Unfortunately, as such it cannot be unequivocally confirmed to be a New Zealand coin, since Rhodesia & Nyasaland used this exact same obverse on its threepences. I'm not sure how common brockages are in either the New Zealand or Rhodesian series.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis






















