It's a busy morning at Jacob & Co. jewelers. The shop's owner, Jacob Arabo, is about to sit down with a visitor when Sean (P. Diddy) Combs, the rapper turned fashion impresario, bursts through the front door with his entourage, including a tiny white dog. After a flurry of activity, the jewelry emergency is over. The star and his companions are sent on their way, the purpose of their mission a closely guarded secret.

The event is pretty typical for the boutique on New York City's East 57th Street. Though Jacob & Co. opened its doors just last December, Arabo's relationship with the entertainment industry spans at least a decade, back to the day when two hip-hop stars discovered the young jeweler toiling at a booth in Manhattan's gritty diamond district. With his bold (some might say flashy) pieces, he's helped transform diamonds from a stuffy blueblood accessory to an indulgence of choice among the young, hip and moneyed. Today the market for rocks couldn't be hotter: worldwide sales broke the $60 billion barrier for the first time last year, an increase of more than 13 percent over 2001, reports the Jewelry Industry Research Institute. And Arabo is taking advantage of the boom. Some 200 stores in more than 30 countries carry his watches and jewelry; now Arabo is planning to open his own shops in Los Angeles, Paris, London, Tokyo and other diamond-friendly capitals. "My goal is to become one of the largest brands in jewelry," he says.

Arabo made his name by designing men's rings and pendants at a time when no one else was. "Other jewelers said, 'You're losing your mind. No one's going to buy that'," he says with just a trace of an accent (he emigrated with his family from Tashkent, Uzbekistan, as a teenager). His inspiration came partly from the '80s hip-hop group Run-DMC, who were prone to wearing massive--but gem-free--rope chains onstage. "I took that business and turned it around and made these big diamond pieces," says Arabo, who himself is modestly dressed in an elegant pin-striped suit. When Faith Evans and her husband, the Notorious B.I.G., happened upon his booth in the mid-1990s, there was an instant connection. Since then, he's earned the nickname "Jacob the Jeweler," been mentioned in dozens of songs by the likes of 50 Cent and Jay-Z, and appeared in several videos.

Arabo's design style today is as glitzy as ever. Though the front of his store holds more-traditional items like engagement rings and vintage-style diamond chokers, the rear is where the serious bling is. Behind one case sits his new Diamond Tourbillon watch, covered with more than 15 carats of diamonds (price: $245,000). Another case displays a rose-gold and diamond pinky ring shaped like a record player, worn by Missy Elliott.

But it gets even better. "People who have everything, they buy diamond toys," says Arabo. He steps out and returns carrying two necklaces the size of cobras. They're for music producer Pharrell Williams and are worth a combined $750,000. One has a white-gold rope chain with a diamond-encrusted pendant shaped like an astronaut's head (the logo for Williams's clothing brand Billionaire Boys Club). Williams plans to wear both at a bash he and Arabo are attending in Moscow. "Russia hasn't seen pieces like this since [Tsar] Nikolai's time!" he raves.

Though Arabo has already achieved an enviable level of success, the 40-year-old still has big plans. "If I were in the music business or in sports [I might be thinking of retirement]," he says. "But I'm just beginning to show you what I can do." Minimalists, take cover.