Pity the poor spinel.

The gemstone that many people have never heard of has been saddled for centuries with the name “the great impostor,” Alessandro Borruso said as he sipped a morning espresso in the cafe of Sotheby’s London offices, where he is head of sales for Europe.

The spinel acquired that pejorative name for good reason. For hundreds of years it was believed that spinels and rubies were the same stone. Indeed, a spinel can be every bit as beautiful as a ruby, Mr. Borruso said, with a rich color that he called “stoplight red.”

And, according to Courtney Stewart, a senior research assistant in the Department of Islamic Art at the Metropolitan Museum of Art, “rubies and spinels are known to be found in the same mines, which would have further confused these two very similar looking stones.”

No wonder no one suspected there was a difference until 1783, when the French mineralogist Jean-Baptiste Louis Romé de l’Isle developed a test that showed a spinel was not a ruby, said Claibourne Poindexter, an associate jewelry specialist at Christie’s New York. And there was still more bad news.

“In 1812,” Ms. Stewart wrote in an email, “Friedrich Mohs published the scale which is still used today to define the relative hardness of gemstones. At that time, ruby (corundum) was identified as a 9, while spinel was realized to be a 7.5 to 8.

“In Europe the hardness associated with gemstones like diamond and corundum contributed to an increase in perceived value for these stones,” she added.

Spinels continued to be used in jewelry throughout the 1800s and early 1900s, but “when people realized it wasn’t really a ruby, it became a Class B gem,” Mr. Borruso said.

Everyone had been fooled. Even royals. “One of the best-known examples lies in the Tower of London,” said Daniela Mascetti, the European chairwoman of Sotheby’s Jewelry Division. It is “an uncut red spinel called the Black Prince’s Ruby which is set on the front of the Imperial State Crown, one of the British crown jewels.”

No doubt about it, the spinel has had a checkered past. But anyone who visited the exhibitions of the Al-Thani jewelry collection at the Victoria and Albert Museum in London, the Grand Palais in Paris or the Met can appreciate how India’s maharajahs prized the gems. “Spinels have been popular in the Mughal Empire due to the proximity of the source,” Ms. Stewart wrote.

Added Ms. Mascetti: “The earliest spinels are thought to have come from Northern India, and actually in early references, spinels were often known as ‘Balas ruby,’ a name most probably derived from the North Indian region of Balascia (or Badakshan.)”

In his office in Paris, Pierre Raniero, Cartier’s director of image, heritage and style, talked about the spinel’s rise and fall. “Cartier has always used spinels,” he said, but less frequently after World War II, when precious stones like diamonds and emeralds were favored.

Then came the big, bold, bling-filled ’80s and “color and big stones became popular again,” he said, and the spinel started making a comeback. “The period when people thought of spinel as a second choice is finished, totally,” he said. “People concentrate on the intrinsic beauty of them. There is no longer any prejudice.”

Rich Shades

Color is really what spinels are all about. Many jewelry makers have used their vibrant, shimmering range of shades to enrich designs.

The London-based jewelry maker Pippa Small, for example, wrote in an email about Sanjay Kasliwal, the late owner of the Gem Palace, “tipping a packet of brilliant pinks and flashing oranges, warm heathers and plum-colored gems on to the table in front of me and being captivated. They were so beautiful. Each stone was hand cut and uneven and in such a rainbow of colors.

“In recent years I’m using spinels even more than before,” Ms. Small continued. “The finest spinels display a bright, vitreous luster. We only use spinels that display a specific shade of red — those that exhibit a strong, even, perfectly saturated hue. When expertly cut, they exhibit a captivating brilliance and exceptional clarity.”

Albert Boghossian, chief executive of the Geneva-based jewelry company that bears his family name, said he was similarly struck by the spinel’s surprising range of colors, writing in an email that it is “a magical stone with its numerous hues and tonalities.”

“We were fortunate enough,” he added, “to own one of the rarest hues ever found in spinel, a cobalt blue Vietnam natural spinel which we subsequently designed into an exquisite ‘Kissing Ring’ and sold it to a gem collector who recognized instantly the extreme rarity and value of this unique spinel.”

Mr. Poindexer of Christie’s said the color is natural: “Their high refractive index gives spinels lots of fire.”

And, Mr. Borruso of Sotheby’s noted that the lack of manipulation is a plus for the gem. “Ninety-eight percent of rubies and sapphires are treated, often heated to change the colors and dissolve some inclusions,” he said. “People have a craving for things that are real. As with food, people want to know where things are coming from, and that they are natural.”

Another reason spinels are enjoying a comeback: There are simply more of them available. “Recently we have noticed a renewed interest in this stone,” Ms. Mascetti of Sotheby’s said, “perhaps sparkled by the discovery of spinel mines in Tanzania and by the continuous quest of jewelry houses to offer something different.”

And as the major source of pink diamonds, the Argyle mine in Western Australia, is scheduled to close at the end of the year, spinels are being considered as an alternative. Mr. Borruso, finished with his coffee, opened a vitrine and pulled out a pair of earrings featuring both pink diamonds and spinels. “You can’t really tell which is which,” he said.

Price also is an advantage. “They are not as expensive as rubies and sapphires but still have similar beautiful colors,” Ms. Small wrote.

While a ruby might go for $40,000 a carat, a spinel of the same size and quality would garner only $1,000 to $7,000 a carat, Mr. Borruso said — which would be appealing for many in the jewelry industry looking for ways to attract younger, and potentially less affluent, buyers.

But the price of spinels has been increasing. “They’re unusual to find at auction, so when they do, people pay attention,” Mr. Poindexter said.

Bidders certainly did at Sotheby’s Magnificent Jewels and Nobel Jewels auction in November in Geneva: A Cartier spinel, emerald and diamond ring, expected to sell for 100,000 to 150,000 Swiss francs, sold for 325,000 francs ($334,500).

And Christie’s had an even bigger score at its Maharajas and Mughal Magnificence sale in June in New York when an imperial necklace of pearls, emeralds and spinel, estimated to sell for $1 million to $2 million, sold for $3,015,000.

No wonder Mr. Poindexter called the spinel “the collector’s gemstone” while Mr. Borruso labeled it “a connoisseur’s stone.”

Either way, the spinel’s days of being called the “great impostor” are over.