I have this lovely little piece, but am not sure what it is or what it is made of. It may be a collar or vest stud. I don't think it is a cufflink, as it is too small. I assume it is gold, but it has no markings. Could it be brass? It is very light and measures 3/8" wide by 3/8" deep.
Definitely a stud of some kind. You may want to get the gold tested and the little pearl. It could be a little seed pearl.
Unfortunately it's hard to tell from a picture.