Ever since Mikhail Baryshnikov’s character gave Carrie Bradshaw that diamond briolette necklace in Sex and the City, I’ve been fascinated by them. You can buy brown briolettes relatively inexpensively because the diamonds are fairly poor quality, generally. Something tells me the ones in the necklace are of a better grade. No carat weight is given, but the estimate for these, on offer May 11 in Geneva from Sotheby’s, is 22,000-32,000 Swiss francs.