Washington, D.C. ? Light flashes across the 82 facets of the Tiffany Diamond, highlighting the brilliance of the giant gem at the Smithsonian’s National Museum of Natural History.

One of the world’s largest yellow diamonds, the stone is on loan from Tiffany & Co., today through Sept. 23.

The Tiffany Diamond weighs 128.54 carats and is in a cushion cut. Perched on it is a gem-encrusted bird known as the “Bird on a Rock,” designed in the early 1960s.

“It’s the largest diamond on public display in the United States,” said Jeffrey E. Post, curator of gems at the museum. It’s more than two-and-one-half times the size of the famed Hope Diamond, which weighs in at 45.5 carats.

Fernandina M. Kellogg, president of the Tiffany Foundation, said the stone is priceless. It has only been worn twice, once by a Rhode Island socialite and once by actress Audrey Hepburn in a promotion for the film “Breakfast at Tiffany’s,” Linda Buckley, a Tiffany vice president, said.

Discovered in 1877 in South Africa, the stone was purchased by New York jeweler Charles Tiffany. His gemologist, George Frederick Kunz, studied the gem for a year before beginning to cut it – reducing it from 287 carats to its current size.