C and Diamond mark on 14k emerald pendant

by Dave B.
(Adelaide Australia)

Hi

I bought this pendant second hand for my 9yo daughter for xmas. She has noticed the hallmark and asked whats that after telling her its a jewelers mark she now would like to know more about it. Like who made it ,when it was made, is it a real emerald etc. So many questions but no answers. any help would be greatly appreciated.
Thanks

Dave