Antique costume jewelry cameo brooch and earring set

by Angela Peoples
(Nashville, TN, USA)

I have looked everywhere. My grandmother passed away and in her jewelry box was a bunch of antique costume jewelry. Among them was a cameo set by the company Whiting & Davis Co. - a brooch and set of earrings. They are set in silver with an opal like background with a black cameo in them. Can you tell me if this is rare, real or how much it is worth?