April 9 (Reuters) - MP Materials said Australian billionaire Gina Rinehart's mining firm has taken a 5.3% stake in the company, adding to her rare earth investments.

In a regulatory filing last week, the Las-Vegas based miner said Hancock Prospecting, owned by Australia's richest person Rinehart, holds about 8.8 million shares of MP Materials.

MP Materials, the biggest producer of rare earths in the United States, had ended talks with Australia's Lynas Rare Earths in February over a potential merger. (Reporting by Roshia Sabu in Bengaluru; Editing by Maju Samuel)