It is an industry that was supposed to be cleaned up, after the turn-of-the-millennium­ notoriety surrounding so-called blood or conflict ­diamonds—precious stones mined in African war zones ...

In December, Yrady proposed to Montiel in Italy with a radiant-cut diamond almost as big as a gummy bear. “Everyone and all of my girlfriends that see it are in love with it,” said Montiel ...