By Jonathan Stempel

NEW YORK (Reuters) - A Tiffany lighting fixture stolen in a still-unsolved 1976 heist from Broadway's Belasco Theatre has turned up in the hands of a Rockland County, New York, woman, and the Shubert Organization, which runs the venue, has sued her to recover it.

In a complaint filed late Tuesday in the state Supreme Court in Manhattan, Shubert said it discovered the fixture after Vilma Partridge consigned it for sale by Lillian Nassau, an antiques gallery specializing in works by Louis Comfort Tiffany and Tiffany Studios.

Shubert said the gallery recognized the bejeweled, slightly translucent fixture, whose colors range from pale yellow to amber to red-orange, as one of five Tiffany lighting fixtures stolen from the Belasco in a Feb. 28, 1976, break-in.

But it said Partridge and her daughter, Anne, a co-defendant and her legal representative, have refused to part with the fixture after Lillian Nassau returned it to them.

While the Partridges are not accused of involvement in the theft, Shubert said that as a matter of state law and public policy, "Vilma never acquired good title to the fixture, and the fixture remains the property of Shubert."

According to the complaint, the fixture is one of the two larger fixtures that had been stolen.

Shubert said it will seek damages if Vilma, of Spring Valley, or Anne, of nearby Pearl River, refuse to turn it over.

The defendants' lawyer did not immediately respond on Wednesday to a request for comment.

A lawyer for Lillian Nassau, located on East 57th Street in Manhattan, did not immediately respond to similar requests. The gallery is not a defendant.

Located on West 44th Street between Sixth Avenue and Broadway in Manhattan, the Belasco opened in 1907 as the Stuyvesant Theatre, and received landmark protection in 1987.

Shubert operates 17 Broadway theaters, including the Broadhurst, Imperial, Majestic, Music Box and Winter Garden.

The case is Shubert Organization Inc v Partridge et al, New York State Supreme Court, New York County, No. 159989/2016.

(Reporting by Jonathan Stempel in New York; Editing by Jonathan Oatis)