The bezel or oval base of the tie tack is 7/8 inch by just about 5/8 inch. The Natural Angelskin coral cabochon is set in a setting of numerous prongs. I do not know the metal content of the setting, but it is yellow gold toned and cast. It does not appear to be plated. Pin back is a standard plated version with short chain and bar.
(I also have a pair of cufflinks being listed with coral a similar color. They go well together, but not the same maker so I have listed separately. If you happen to get both I can combine shipping.)