WASHINGTON (AP) – Tiny fireworks seem to go off inside the deep red stone as it turns, flashes of light reflecting off the facets of one of the world’s largest rubies.

The Carmen Lucia ruby goes on public display for the first time Saturday, the newest star of the National Gem Collection at the Smithsonian’s National Museum of Natural History.

The 23.1 carat stone “is the largest and finest faceted ruby on public display,” Jeffrey Post, curator of the gem collection, said Tuesday.

Discovered in Myanmar-which was formerly known as Burma – in the 1930s, the stone has been in private hands until now.

Post said that when he first saw it a few years ago, it took his breath away.

The gem, set in a platinum ring with diamonds, was obtained with funds donated to the museum by Dr. Peter Buck in memory of his wife. Post declined to discuss the price.

“The Carmen Lucia ruby is a breathtakingly beautiful gemstone and a magnificent gift to the American people,” Post said. If it had been sold privately, chances are it never would have been available for public viewing, he said.

It’s not as big as the famed Hope Diamond or some other stones but it is about as big as rubies get, Post said.

And the fiery light reflected from the ruby easily draws attention away from the larger sapphire that will be displayed nearby.

The two types of stone are displayed together because they are essentially the same material – corundum, or aluminum oxide – Post said. The ruby gets its red color from traces of chromium, while other materials give the sapphire its usual blue color.

Post added that some large red gems are on display in various collections labeled rubies, but many of them are actually spinels, a different type of stone that is also red. While rubies are aluminum oxide, spinels are magnesium aluminum oxide. Spinels look like rubies and attracted much interest in the past because they tend to be larger, he said.

It’s impossible to set a value on the new gem, Post said, commenting that as a large, clear stone becomes better known more people become interested in it and it becomes, essentially, priceless.

Post said Mrs. Buck, a native of Brazil, was proud of having become an American citizen. After her death her husband, a co-founder of the Subway sandwich shop chain, decided to arrange for the museum to acquire the gem as a gift to the nation in her memory.

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