By Amanda Breen Tiffany & Co. is currently selling its most expensive piece of jewelry ever. “The World’s Fair Necklace,” unveiled in Dubai on Sunday, boasts a dazzling 180 carats of diamonds set in platinum. The 578 total diamonds include 353 round brilliant cut stones and 224 custom-cut baguettes. The centerpiece is an 80-carat oval, flawless D-color (highest grade and virtually colorless) “Empire Diamond,” getting its name from the Empire State Building in the retailer’s city of origin, New York. The Empire Diamond was ethically sourced in Bostwana, cut and polished in Israel, then set in the jeweler’s New York City workshop. Related: Tiffany Cuts Jobs as Sales Lose Sparkle The centerpiece in the World’s Fair Necklace can also be converted into a ring; a Tiffany jeweler will be on call to mount it onto platinum whenever the wearer chooses. Although the iconic jeweler has yet to reveal the price of the piece, industry experts estimate the cost is between $20 million and $30 million. …