December’s birthstone, turquoise, comes in many forms — the most notable being pristine sky blue.

At the Smithsonian’s National Museum of Natural History, visitors can see pieces of this type of turquoise, called Persian turquoise, in a diadem once owned by Napoleon’s second wife, the Empress Marie Louise.

“The Marie Louise diadem is one of the few spectacular jewelry pieces that survived that era. It represents that period of time in history, showcasing the symbolism and role gems played back in the early 1800s,” said Jeffrey Post, mineralogist and curator-in-charge of gems and minerals at the museum. “But the turquoise pieces were actually latecomers to the diadem.”

During the 1950s, jewelers replaced the diadem’s original emeralds with 540 carats of Persian turquoise, turning it into the piece now on display in the museum’s Janet Annenberg Hooker Hall of Geology, Gems and Minerals.

“The gems in these jewelry pieces change over time and those changes become part of their story. Generations of people have seen this diadem with the turquoise, and that’s its own story now,” said Post.

Raining turquoise

Turquoise forms when rainwater trickles down into the veins of rocks close to the Earth’s surface. As the water travels, it carries copper and phosphate minerals through those veins. The minerals build up over time and become a turquoise deposit.

“Water from rainfall fills cracks and crevices on the surface, percolating down and dissolving copper and other minerals in an area,” said Post.

Some turquoise has grey webbing, which happens when other minerals accumulate in deposits with the turquoise. Other turquoise is pure blue because the copper and phosphates come together without any disruptions.

While types of turquoise have been used as gems and ornamental stones since before the ancient Greeks, the type without grey webbing traditionally came from Persia. In the Late Middle Ages, it was traded through Turkey, earning its name “turquoise” from the French word for the country. For Europeans, Persian turquoise’s pure, sky-blue appearance became the standard for quality.

But no matter the type, all turquoise is fairly soft compared to other minerals. This made it easier to cut and shape when jewelers decided to switch out the gems in the Marie Louise diadem.

“Turquoise is hard enough to polish and soft enough to shape or cut. One of the reasons the jewelers picked the gem to replace the diadem’s emeralds is that they could fairly easily shape the turquoise to match the diadem’s settings and holes,” said Post.

Handmade history

While the Marie Louise diadem now sparkles with Persian turquoise, it originally held 79 emeralds from Colombia. Napoleon chartered the emerald diadem, along with a necklace, earrings and comb, in 1810 as a wedding gift.

“It’s an incredible example of the kind of jewelry work that was being done in the late 1700s and early 1800s, where it would have been done by hand,” said Post. “Pieces like the diadem often involved thousands of hours of work to make.”

Since then, the necklace and earrings — with original emeralds intact — went to the Louvre. The comb was disassembled for its gems, while the diadem was passed through Empress Marie Louise’s family until they sold it. During its journey, the diadem lost its emeralds and gained 79 Persian turquoise gems. Its 1,006 diamonds remained.

“The fact that this diadem has been preserved — other than its emeralds being taken out and turquoise being put in — makes it a great piece of history that shows you the methods and skills it took at the time to create something like this,” said Post.

A portal to the past

Since 1971, the diadem has rested in the National Museum of Natural History. Although its appearance has changed over the centuries, it continues to offer visitors a snapshot of the natural world’s beauty.

“There are very few things that we interact with in this world that will be just the same a million years from now,” said Post. “But the turquoise and those diamonds are going to be just as beautiful and sparkly as they are today.”

Besides its beauty, the diadem is equally important because of its global history. It’s a rare relic from Napoleon’s tumultuous reign. Being on display allows people to connect with that period in a tangible way.

“A big part of any story for any jewelry piece is its provenance, or its history. The fact that this was a gift to the Empress in and of itself makes it important,” said Post. “Looking at the diadem can give visitors a portal to look back in history and picture what it was like at the time.”

Related Stories:
The Story Behind the New 8,000-Pound Quartz at the Smithsonian
The True Story Behind How Pearls Are Made
How the World’s Largest Aquamarine Gem Came to Be
Get to Know the Hope Diamond’s Keeper