An ultra-rare “Ides of March” gold coin commemorating the assassination of Roman dictator Julius Caesar in 44 BC broke an auction record Thursday when it fetched $4.2 million at London-based Roma Numismatics Limited. The selling price, which includes a buyer’s premium, was more than six times the pre-auction estimate of...

The “Diavik Helios,” a 74.48-carat fancy yellow diamond named after the mythical Greek God of the Sun, headlines Rio Tinto’s forthcoming “Specials” Tender — a selection of the largest and finest rough diamonds from the company’s mines in Canada and Australia. The 2020 Specials Tender is especially significant because it...

Quartz is one of the most abundant minerals in the Earth’s crust, and in its pure state it is colorless. But when trace amounts of iron (about 40 parts per million) mix into quartz’s chemical makeup, extraordinary things happen. The colorless silicon dioxide emerges as citrine in a gorgeous array...

At first glance, the shiny yellow stone that emerged from Steven McCool’s 11th — and last — bucket of the day at Crater of Diamonds State Park seemed to be a well-worn piece of amber-colored glass. But then it quickly dawned on the Fayetteville, AR, native that the jelly-bean-size curiosity...