14K gold and black onyx tie tack.
The face of the tie tack is 1/2 inches by 3/8 inches, and the head weighs 1.2 grams.
Marked on the back and also on the pin stem with "14K".
Very good condition. Note that the "attachment" component is not gold--just the tie tack itself.
14K Gold & Black Onyx Tie Tack