Kirk Johnson, the new director of the Smithsonian National Museum of Natural History, gazes at the 10,363-carat Dom Pedro aquamarine. (Marvin Joseph/THE WASHINGTON POST)

For a few more days, until Thursday, the Smithsonian’s newest and perhaps most stunning earthly treasure hides behind a thick metal door, like that of a bank vault, deep in the heart of the National Museum of Natural History, behind the galleries, beyond the cabinets stuffed with chunks of minerals, deep inside the “blue room,” whose shelves groan under heavy crystals of a thousand sparkling hues.

The museum’s longtime curator of gems and minerals, Jeffrey Post, handles an unmarked white box. It’s the right size and shape to hold, say, a tall bottle of the world’s finest Scotch. Post marches the box into the blue room, so called for the thick carpet, and also the color of the cloth draped across a chest-high cabinet, upon which he sets the box.

Post dons a pair of white cotton gloves. Unlatches two clasps. Opens the lid.

“This,” announces Post, “is Dom Pedro.” Post enunciates with a flourish, bouncing along the final syllables. “You have to use the Portuguese accent,” he says with a laugh and a nod to the gem’s Brazilian origins.

The museum’s new director, Kirk Johnson, is leaning against the cabinet. He lets out a low whistle.

The largest aquamarine in the world, called Dom Pedro, is 14 inches tall and weighs 10,363 carats. That’s the heft of a barbell, nearly five pounds. (Lichtblick Fotodesign/LICHTBLICK FOTODESIGN)

This is Johnson’s first glimpse of the glittering azure obelisk, as clear and blue as the Caribbean at noon.

Unboxed and upright, Dom Pedro towers like a gemmy Washington Monument.

It’s the largest cut piece of aquamarine ever known — perhaps 10 times the size of the next largest. It’s 14 inches tall and weighs 10,363 carats. That’s the heft of a barbell, nearly five pounds.

It’s a gift of the earth, sculpted by a master cutter into a gem of outlandish proportions.

“Look at the clarity. Look at the color of the aquamarine here,” says Post.

The eye cannot rest on Dom Pedro. It is drawn upward to the pyramid tip by an eight-fold set of climbing carved starbursts that flare and shimmer like the beating wings of iridescent angels.

Dom Pedro’s sculptor, the German gem artist Bernd Munsteiner, strives for “total reflection,” Post says. Most gems are faceted on the outside — like the typical brilliant or diamond cuts seen in jewelry. Munsteiner instead cuts into his gems, sculpts internal facets to bounce every beam of gathered light back at the viewer.

Goal achieved.

“Think of the gemstones that could be cut from a piece like that,” says Post. “There’s millions of dollars worth of aquamarine in there.”

The bluest aquamarines rival emerald in value, but Dom Pedro may as well be priceless. It’s off the market forever, donated to the Smithsonian Institution last year by a collector couple from Palm Beach, Fla., Jane Mitchell and Jeff Bland.

On Dec. 6, Dom Pedro — named after the first emperor of Brazil — will go on permanent display. Under spotlights in the entrance to the national gem collection gallery, Dom Pedro will shine like a beacon, a rival to the most famous gem in the world, resting not 30 feet away, the Hope Diamond.

“This piece will become one of the highlights for the Smithsonian,” said Jürgen Henn, a German gem broker, former co-owner of Dom Pedro, and the force behind its creation. “It is strong competition for the Hope. In rarity and purity, it is at least the same.”

Like every gemstone, Dom Pedro’s story begins in the craggy crust of the earth. A sister to emerald, aquamarine crystals are born in mineral-rich water. The first step is the trickiest: atoms of silicon, beryllium, aluminum and oxygen must join together in a molecular handshake. When they do, they form a hexagonal pattern. This nucleus makes a template. As mineral-rich waters flow, a torrent of atoms piles on, each following the plan, snapping into place like Lego bricks, elongating the crystal. If the source water holds traces of chromium, the mineral grows green — that’s emerald. But the part of the Earth that grew Dom Pedro held iron instead, whose inclusion turned the crystal blue: aquamarine, spirit of the sea, treasure of mermaids, protector of sailors.

If the temperature and other conditions stay steady, and if the chamber in which the mineral waters run is large enough “you grow a big crystal,” said Post.

When found, the Dom Pedro crystal stretched more than three feet long and weighed something close to 100 pounds. Sometime in the late 1980s a garimpero, or prospector, spied it. He and two buddies pried it loose and lugged it out of a mine in the state of Minas Gerais, famous for its gemstones. The garimperos dropped the crystal, shattering it into thirds, a seeming disaster that later proved serendipitous, indeed, crucial, to the carving of Dom Pedro.

The mine’s owner took possession. He sold the top two chunks, which were cut into typical jewelry. He kept the third, and largest, piece — still close to two feet long and 60 pounds — behind his bed. Or so the story goes.

Henn, a third-generation broker and dealer, soon heard of this monster crystal. Since the 18th century, at least, Henn’s hometown of Idar-Oberstein, nestled in the mine-pocked hills of Rhineland, has been a European gem center. After Brazil opened up as a rich land of gemstones, the town’s dealers built connections there. Or, as Henn says, “Whenever something big goes on, you get wind. You get phone calls.”

Henn met the mine owner at his home. “I’ll never forget it,” said Henn. “It was exactly high noon. I mean, wow, really. It was offered to me in a backyard, on a simple table. It was a matter of a second. You saw the thing — that’s it!”

Henn hatched a plan. His philosophy: Whatever the earth makes big, man should not make small.

Only one gem cutter could handle such a piece: Bernd Munsteiner, Henn’s lifelong friend and business partner. In the 1970s and 1980s, Munnsteiner pioneered a new style, eyeing big crystals as Michaelangelo would a block of granite — with a sculpture inside. Crystals were art waiting to happen.

“Munsteiner is a real pioneer” of big gemstone sculptures, said Russell Shor, senior industry analyst for the Gemological Institute of America.

But first, Henn had to acquire the crystal. He partnered with Munsteiner and a second well-known dealer, Hermann Bank. In 1992, Henn dispatched his son Axel and Munsteiner’s son, Tom, to make a deal, according to an article in a 1995 issue of the Lapidary Journal.

The younger Germans engaged in lengthy negotiations with the mine owner. But the owner was in no hurry. He flew the Germans to a remote river for a week of fishing.

Henn, at his showroom in Idar-Oberstein, was handling calls from Brazil as negotiations wound tighter and tighter. Just then, Jane Mitchell, an American businesswoman and budding gem enthusiast, arrived.

“I had no idea how to find a showroom for Munsteiner,” Mitchell said. “You don’t see what’s going on in Idar-Oberstein. They stay in the background.” You need connections.

She eventually gained entrée after a gem dealer in Zurich handed her Henn’s calling card.

“That contact opened doors to an Aladdin’s cave of the wonderful treasures and work that’s gone on for hundreds of years there,” Mitchell said.

And she just happened to arrive at the climax of the biggest deal of Henn’s life.

“They were making decisions about whether the stone was stable enough, had qualities to stand up to cutting, was it the right price to pay,” said Mitchell.

Deal done, the German sons spirited the crystal out of Brazil. The Lapidary Journal article by Si and Ann Frazier paints a Hollywood scene. They hired sketchy pilots, bribed a few customs agents, persuaded a Brazilian general to shut down the Rio airport as the crystal landed in a small plane, stashed the thing in the control tower, and nonchalantly-as-can-be-toting-60-pounds hauled it aboard a Lufthansa flight in a duffel and stuffed it in the overhead bin.

Or so the story goes.

The artist Munsteiner then set to work. He agreed to the audacious job for one reason only. The shattering of the original crystal, he was convinced, had relieved any hidden stresses, made the largest chunk strong enough to withstand his diamond blades.

For four months, Munsteiner eyed the azure monster.

“He made sketches, created ideas, designs, his whole seating room was filled with designs,” said Henn. “He slept with the ideas.”

Munsteiner settled on a plan. He would shape an obelisk, preserving as much of the original length as he could. Into the backside, he would excavate dozens of spiky “negative cuts,” the ascending starbursts, to achieve total reflection.

The cutter toiled for six months. He worked for just two hours a day to keep his mind clear, his arms strong. A treasure was his to create — or, with a slip, to destroy.

Each lengthwise buzz of the blade, said Post, shaved a quarter of a million dollars of aquamarine into dust. The sewers of Idar-Oberstein ran rich for weeks.

In 1993, Henn and Munsteiner unveiled Dom Pedro in Basel, Switzerland. The German government then showed it off around the world.

Mitchell, who kept up with Dom Pedro’s development, arranged one showing in Palm Beach in 1996. There, she finally saw Dom Pedro naked, no glass between. “The color, somehow the color, it’s beautiful, I could lose myself in the color,” she said. “The light glows through it.”

Three years later, opportunity arrived for Mitchell.

The Brazilian miner — still part owner — needed cash. He was threatening to cut the stone into a thousand pieces.

The German consortium needed a buyer. At one point, a member approached Post at the Smithsonian, Dom Pedro in hand. He asked for “seven or 10 million dollars,” Post says. He remembers laughing: It doesn’t work like that. The Smithsonian collects via donations. “We can’t just go to Congress and ask for $10 million for a gem,” he said.

An offer did arrive, said Henn. But it was not quite the right deal. Saudi sheiks, the sultan of Brunei — they were big into Munsteiners. But they kept their treasures to themselves, mostly. Out of public view. Dom Pedro, Henn felt, belonged to the world. He wanted it in the Louvre or the Smithsonian, and strived for an owner who concurred.

He called Mitchell.

Again: Timing is everything. Mitchell and her husband had recently sold their booming surgical tool company, called Midas Rex, for a healthy sum.

They slept on it.

They bought it.

They saved Dom Pedro.

“We didn’t buy it for ourselves,” said Mitchell. “Our motivation was, ‘Oh, you can’t cut that up.’”

Before donating Dom Pedro, Mitchell and Bland displayed it two of the last 13 years, in Houston and Paris.

At the Ecoles de Mines in Paris, a top gem school, experienced viewers, professors of gemology, saw Dom Pedro and asked: How do you get it to glow? Where is the light?

The light bulb was in Mitchell’s head. It lit up.

“That’s when it dawned on us we were looking for a museum. That awe belongs to all of mankind — it’s part of the awe of the natural world,” she said.

Mitchell views Post as Dom Pedro’s final guardian.

Over annual lunches at the huge Tucson Gem and Mineral Show, Post had gained Mitchell’s trust. She felt he would take care of Dom Pedro, display it as a world treasure to the museum’s seven million annual visitors.

Mitchell will be at the museum Thursday to help pull back the curtain.

“Every time I see it, it’s more beautiful than I remember,” she said. “I carry a picture in my mind, but when I see it in person every time, I just go, ‘Wow.’ It’s even better.”

Dom Pedro will be unveiled at 11 a.m., Thurs. Dec. 6, in the National Gem Collection Gallery on the second floor of the Smithsonian’s National Museum of Natural History.