These cufflinks are an octagon of dark mother of pearl set into a 9 karat white gold engraved edge.  The mother of pearl has a brownish color and has an iridescent glow of pink and green.  From the Deco period of the 1920's, these cufflinks have a chain link and measure 1/2" across.    The studs are not gold and are unmarked.  They measure 5/16" across.

 

Another view of the cufflinks alone: