Art Deco Onyx and Marcasite Sterling Silver Ring

Very pretty Art Deco style ring in great condition for age. One support bar is a little bent, but not noticeable when worn. The stone is very dark and opaque. I think it is onyx. I’m not a jeweler—just know what I was told. Some scratches and lots of patina. 28mm long and 16mm wide. Estimated to be a 6.5 in size.