You almost never want to get the boot. Except that on the second Friday in June, passionate collectors from all around the world will be clamoring for it.

The boot in question obviously isn’t a pink slip or a rejection notice. It’s the largest surviving natural gold nugget found in the Western Hemisphere—nicknamed the “Boot of Cortez” for its distinct boot-like shape—and it will cross the block during a dedicated sale led by EJ’s Auction & Appraisal in Glendale, Arizona. Coincidentally, the auction location is only about 200 miles north of the site where the nugget was originally discovered. Talk to any specialist or informed collector of natural history and they’ll all say the same thing: The specimen is incredible. However, the story of its discovery is no less remarkable.

In 1989, an amateur treasure hunter from Mexico, armed with just an entry-level metal detector—a device he purchased at Radio Shack, of all places—ventured to a parcel of the Sonoran Desert near the town of Caborca and close to Gran Desierto de Altar. The barren landscape, despite its harsh conditions (daytime temperatures often exceed 125 degrees Fahrenheit), was—and still is—famous for its connection to many legends of treasure. It seems that every village in the area, no matter how remote, clings to its own tales of lost mines and well-hidden troves of riches: the Oro de Moctezuma, Tayopa, and El Naranjal, among others.

As the story goes, this particular treasure hunter spent several days in those harsh conditions, carefully following a pre-determined grid pattern to ensure every square foot of the desertscape was scanned. Every now and then, the hunter’s headphones would ping, registering a metallic hit below ground; though the vast majority of those signals were inconsequential, identifying only bits of scrap iron or old lead bullets. Finally, the hunter heard a “beep” with a notably different pitch, and after digging for a short while, he uncovered a portion of this nugget. Yet, his surprise (and delight) continued to grow as he continued to dig and more of the specimen was uncovered.

In its entirety, the nugget, which measures 10 ¾ inches high and 7 ¼ inches wide, weighs 383.10 troy ounces—more than 26 pounds! Equally staggering is its size in comparison to the next largest gold nugget found in the Western Hemisphere. That specimen, which was uncovered in Alaska, is 100 ounces lighter. And while larger masses of gold have been discovered over the years, all others have consisted mostly of intermixtures of gold and valueless rock. The Boot of Cortez, on the other hand, is 98 percent pure gold, and its rich, luminous hue exemplifies that composition. Not only is this artifact treasure in the highest regard, it looks like treasure too.

EJ’s Auction & Appraisal is confident in all those figures, largely because the firm arranged for an independent third party to weigh and analyze the specimen using a scale certified by the state of Arizona and an X-ray fluorescence (XRF) machine.

Since its discovery, the Boot of Cortez has enjoyed its time in the spotlight. Celebrated as one of the most significant mineral finds of the modern era, the rare mineral deposit has been exhibited at several noteworthy events and institutions, including the Houston Museum of Natural Science and the American Museum of Natural History in New York City. During that world tour of sorts, the Boot of Cortez has earned the distinction of being “the most unusual and attractive large nugget in the world.”

For almost two decades, the Boot of Cortez has not changed ownership. The last time the specimen crossed the auction block, in 2008, it sold for more than $1.3 million—four times the gold spot value at the time. Presently, the value of gold is five times what it was 18 years ago, which offers a glimpse at what the nugget might command this time around.

Until “the boot” crosses the block on June 12 at 1 p.m. local Arizona time, there’s no way to know just how much its value has changed. However, the opening bid is set at $1 million, and the auction house estimates that the historic gold nugget will realize between $3 million and $7 million, not including the buyer’s premium.

“I’m excited to see this magnificent piece find a new home after 18 years,” says Erik Hoyer, the auction house’s owner and CEO. “And we are honored to represent this private estate in auctioning such a rare and historic natural gold formation.”

Bidding registration is open through June 9, and EJ’s will schedule private viewings for collectors who have met the bidder’s criteria. More details can be found at bootofcortez.com.