This ring offered by Brilliant Earth is a reproduction Art Deco style piece. The diamond size details are a bit sketchy; the company notes,This Art Deco reproduction ring features a scintillating round diamond center in a platinum setting. Forty-eight French cut emeralds contrast with twelve faceted onyx accents for a truly dramatic look (approx. 1.87 total carat weight).”
Given the USD$21,840 price, I would expect that the centre diamond has some impressive size/specs to go along with the price tag. Worth contacting them to suss out the details if you are interested.