Aron Weingarten brings the yellow diamond up to the stainless steel jeweler's loupe he holds against his eye. We are in Antwerp, Belgium, in Weingarten's marbled and gilded living room on the edge of the city's gem district, the center of the diamond universe.

Nearly 80 percent of the world's rough and polished diamonds move through the hands of Belgian gem traders like Weingarten, a dealer who wears the thick beard and black suit of the Hasidim.
"This is very rare stone," he says, almost to himself, in thickly accented English. "Yellow diamonds of this color are very hard to find. It is probably worth 10, maybe 15 thousand dollars."
"I have two more exactly like it in my pocket," I tell him.

He puts the diamond down and looks at me seriously for the first time. I place the other two stones on the table. They are all the same color and size. To find three nearly identical yellow diamonds is like flipping a coin 10,000 times and never seeing tails.
"These are cubic zirconium?" Weingarten says without much hope.

"No, they're real," I tell him. "But they were made by a machine in Florida for less than a hundred dollars."

Weingarten shifts uncomfortably in his chair and stares at the glittering gems on his dining room table. "Unless they can be detected," he says, "these stones will bankrupt the industry."

Put pure carbon under enough heat and pressure - say, 2,200 degrees Fahrenheit and 50,000 atmospheres - and it will crystallize into the hardest material known. Those were the conditions that first forged diamonds deep in Earth's mantle 3.3 billion years ago.

Replicating that environment in a lab isn't easy, but that hasn't kept dreamers from trying. Since the mid-19th century, dozens of these modern alchemists have been injured in accidents and explosions while attempting to manufacture diamonds.

Recent decades have seen some modest successes. Starting in the 1950s, engineers managed to produce tiny crystals for industrial purposes - to coat saws, drill bits, and grinding wheels.

But this summer, the first wave of gem-quality manufactured diamonds began to hit the market. They are grown in a warehouse in Florida by a roomful of Russian-designed machines spitting out 3-carat roughs 24 hours a day, seven days a week.