July 16 (Reuters) - MP Materials MP.N said on Wednesday it would sell $500 million of its common stock, a day after the U.S. rare earths miner inked a supply deal with Apple AAPL.O.

Shares of MP Materials fell 5.8% in extended trade. They have surged 275% so far this year, giving the company a market value of $9.57 billion.

The $500 million agreement with Apple is a coup for MP and a rare investment by a tech company aiming to reduce its supply risks for rare earth magnets.

The Las Vegas-based company also signed a multibillion-dollar agreement with the U.S. Department of Defense last week as the government seeks to reduce its reliance on China, which restricted rare earths exports in April in response to President Donald Trump's tariffs. Though the U.S. and China reached a deal in June that has resolved much of the rare earths dispute, broader trade tensions continue to underscore demand for non-Chinese supply.

The Pentagon deal did not require MP Materials to issue stock for the general public.

MP said it intends to use net proceeds from the offering to fund growth opportunities and for general corporate purposes.

The company said it would grant underwriters a 30-day option to purchase up to an additional 15% of its shares.

J.P. Morgan and Goldman Sachs are acting as lead joint book-running managers in the stock sale, while Morgan Stanley is another book-running manager.