Could This 10ct. Blue Diamond Sell for $30M at Sotheby’s?

Sotheby’s will offer a ring with a 10.03-carat blue diamond at its upcoming Geneva jewelry sale, pricing it in “the region” of $20 million, but dealers think it will fetch more.

The Mediterranean Blue, a cushion modified brilliant-cut, fancy-vivid-blue, VS2-clarity, type IIb diamond, will be a headliner at the May 13 High Jewelry sale, Sotheby’s said Wednesday. The auction will mark the…