UPDATE 2-MP Materials swings to quarterly loss on falling rare earths prices

(Adds CEO response to Lynas merger talks in paragraph 3, Vietnam investment in paragraph 11)

Feb 22 (Reuters) - Rare earths miner MP Materials on Thursday reported a fourth-quarter loss due to slipping prices for the strategic minerals and rising production costs, although the loss was not as much as analysts had expected.

The company, which held unsuccessful merger talks earlier this year with rival Lynas Rare Earths, has struggled in recent months with falling prices and stiff competition from Chinese rivals.

Jim Litinsky, the company's CEO and largest shareholder, declined to directly discuss the merger talks on conference call with investors, but said: "Objectively, when you look at any company in a generic sense, there are always things that companies can learn from each other and cut costs around."

Shares of the Las Vegas-based company rose slightly in after-hours trading after falling 2.7% on Thursday.

MP posted a quarterly net loss of $16.3 million, or 9 cents per share, compared with a profit of $67 million, or 36 cents per share, in the year-ago quarter.

Excluding one-time items, MP lost 2 cents per share. Analysts expected a loss of 4 cents, according to LSEG data.

For the past four years, MP has processed rock it extracts from its Mountain Pass mine in California into rare earths concentrate that is shipped to China for refining. The company sold 7,174 metric tons of that concentrate during the quarter, about 34% lower than the year-ago period.

MP said the drop was due in part to lower production at the California mine, partly due to problems at the facility's power plant.

MP has been working to refine its own rare earths for some time. The company said its refining equipment in California produced 150 metric tons of neodymium and praseodymium - the two most in demand rare earths - during the quarter, with 10 metric tons sold.

MP also said it has finished construction on a rare earths magnet plant in Texas and has begun testing equipment there.

The company on the conference call also announced an investment in a rare earths metal facility in Vietnam, where it said it has begun production. (Reporting by Ernest Scheyder Editing by Bill Berkrot)