In 1622, a ship called the Nuestra Señora de Atocha sank in a hurricane—with a 6.25-carat emerald, among many other treasures, on board. Soon, that emerald will be sold at Sotheby’s Magnificent Jewels auction, where it is expected to fetch between $50,000 and $70,000.

The Atocha was a vessel commissioned to support Spanish colonization, and it was returning from an expedition in Havana when it ran into the hurricane and sank. Another vessel, the Santa Margarita, met the same fate. The ships remained underwater near what is now Florida for over 300 years.

In the 1960s, treasure hunter Mel Fisher discovered the Santa Margarita near Florida’s coast. Finally, in 1985, Fisher and his team of treasure hunters uncovered the main hull of the Atocha—and with it, a trove of valuables. In addition to 70 pounds of Colombian emeralds, the ship contained 180,000 silver coins, 24 tons of Bolivian silver, 125 gold bars and a collection of Venezuelan pearls.

Following Fisher’s initial discoveries, the state of Florida laid claim to the treasures. But after a lengthy legal battle, a United States Supreme Court ruling gave all rights to the treasure hunters in 1982.

One of the expedition’s funders was Frank Perdue, the late CEO of Perdue Farms. He received a cut of the Atocha’s treasures, which were worth over $1 billion in total. Perdue donated the majority of his share to the Smithsonian Institution and Delaware Technical Community College, but he kept one item—an emerald—which he fashioned into an engagement ring. He used it to propose to the woman who became his wife, Mitzi Perdue, in 1988.

“Although Frank donated just about all the coins and other artifacts that he received from the Atocha … he held onto this one piece,” Mitzi says in a statement on her website. “Since he was someone who was entranced with the romance of history, I’m not surprised that he kept the emerald.”

Now, Mitzi is bringing the emerald to auction in order to support humanitarian efforts in Ukraine. She is keeping the ring’s band. Mitzi visited Ukraine over the summer, and the trip compelled her to part with her “most precious possession,” she adds.

The emerald originally came from Colombia. As Sotheby’s specialist Alexander Eblen tells Artnet’s Vittoria Benzine, “Emerald deposits have naturally evolved over the course of centuries, so to have one dating back to the 17th century, or defined as ‘old mine,’ is exceptionally rare to come by.”