De Beers is introducing a new line of man-made diamonds, which will range in price from $200 to $800. (Courtesy of Lightbox)

De Beers, the diamond giant that for years has promoted gemstones as pricey and precious, said it will begin selling man-made diamonds that cost about a tenth of the price of a mined gem.

The line of pink, blue and white laboratory-grown diamonds, which De Beers will sell under a new brand, Lightbox Jewelry, is designed to persuade shoppers to think of synthetic diamonds as a “fun piece of fashion jewelry” instead of a lifelong investment, executives said. Prices will start at as low as $200 to appeal to a new generation of shoppers.

“We see this is as opening up new gifting occasions where perhaps a natural diamond would say too much or, frankly, be too expensive,” said Steve Coe, general manager of Lightbox Jewelry. “This is something you might buy for a best friend or for a Sweet 16.”

The shift to synthetic is an unexpected move for the world’s largest diamond miner, which for decades has relied on the perceived scarcity of mined diamonds to drive up values and has railed against synthetic diamonds as one of the biggest threats to the industry.

But now, after 70 years of telling consumers “a diamond is forever,” De Beers is rethinking its message.

The line of man-made diamonds “may not be forever, but is perfect for right now,” Bruce Cleaver, chief executive of De Beers Group, said in a statement.

The lower-priced jewelry is as much about changing consumer habits and preferences as it is about economics, industry experts say. Today’s 20- and 30-somethings — bogged down by heavy student debt loads and stagnant wages — have less spending power than their predecessors did, but they have different values, too: A recent study by De Beers found that millennials would rather splurge on overseas holidays, weekend getaways and electronics than on diamonds.

Lab-grown diamonds — which are created in hot, pressurized chambers over weeks, instead of a billion years underground — have been growing in popularity as Americans spend less on traditional diamonds. The stones are increasingly marketed to younger shoppers as a cheaper, ethically sourced alternative to mined diamonds. But their chemical makeup is the same (all diamonds are made of just one element: carbon), and experts say they are indistinguishable to the naked eye.

“From our perspective, synthetic diamonds are diamonds,” Stephen ­Morisseau, a spokesman for the Gemological Institute of America, a nonprofit organization that oversees the international diamond grading system, told The Washington Post last year. “They’re not fakes. They’re not cubic zirconias. They have all the same physical and chemical properties of a mined diamond.”

Sales of traditional diamonds have stalled in recent years, leading to a steady drop in prices. Overall, the price of high-quality diamonds has fallen by as much as 80 percent over the past 30 years, when adjusted for inflation, according to the RapNet Diamond Index, an industry benchmark. This year, De Beers says it has seen a 6 percent drop in rough-diamond sales.

“It is clear that volatility in the diamond sector is not a short-term phenomenon but the new normal,” Cleaver wrote in a 2016 De Beers report. “The pace of change is quickening and, as a sector, we cannot look to the past for solutions to tomorrow’s challenges.”

With Lightbox Jewelry, De Beers says it hopes to tap into a new market. The line will include earrings and necklaces — but no engagement rings — that cost between $300 to $900, making it a more affordable alternative to traditional diamonds. Plus, executives say, the pink- and blue-hued stones add an element of whimsy. (“In natural diamonds, colored stones are very rare and extremely expensive,” Coe said.)

Although De Beers has long resisted selling jewelry made with synthetic diamonds, it has been creating lab-made diamonds for industrial use for more than 50 years. The company’s Element Six business, based in England, is the world’s largest supplier of lab-grown diamonds for drilling, mining and semiconductors.

That expertise, the company says, allows it to undercut its competitors on the price of lab-grown diamonds. (At the Diamond Foundry, a California-based company that counts actor Leonardo DiCaprio among its investors, for example, one-carat synthetic diamonds start at about $3,500 — more than four times what Lightbox plans to charge.)

“We want to be transparent but accessible,” said Coe of Lightbox. “What we’re doing is giving consumers what they want: diamonds that are new and different, at an affordable price.”

Lightbox Jewelry will be available online in September, and executives say they plan to sell the line in stores by the end of the year. The stones are created in the company’s labs in the United Kingdom, although De Beers is also investing $94 million in a new production facility near Portland, Ore., that is expected to open in 2020.

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