A necklace by the American sculptor Alexander Calder, which was purchased at a flea market for $15 in 2005, will be sold at Christie’s this fall. The brass necklace from 1938 is expected to bring between $200,000 and $300,000.

Philadelphia resident Norma Ifill spotted the rare necklace while she was browsing a local flea market. She was drawn to the piece’s tribal aesthetic but it wasn’t until she visited a Calder jewelry exhibition at the Philadelphia Art Museum that she realized she had a true treasure in her possession. Ifill spoke with the exhibition’s curator and later took the necklace to the Calder Foundation in New York, where her find was deemed a genuine Calder. She also learned that the piece was once on display at the Museum of Modern Art.

The necklace will be offered on September 26, 2013 at Christie’s Post-War and Contemporary Art auction.