NEW YORK—Signed pieces of Cartier and Tiffany jewelry belonging to a late Montana copper mining heiress have sold for nearly $21 million at a New York City auction.

Christie's said Tuesday's sale from the estate of Huguette Clark had caught the attention of collectors worldwide. The star of the collection, a rare pink cushion-cut 9-carat diamond ring, sold for nearly $16 million.

The auction house had estimated the collection of 17 pieces would bring between $9 million to $12 million.

The reclusive Clark was 104 when she died last year at New York's Beth Israel Medical Center. Her father was U.S. Sen. William A. Clark, once one of America's wealthiest, building a fortune from mining copper and railroads.