Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Molycorp (NYSE: MCP) finished trading today up 12%. Molycorp "focuses on the production and sale of rare earth oxides (REOs) from stockpiled feedstocks."

So what: There's no direct news from the company today, but shares likely popped because of several wire stories about China's decision to cut rare earth exports. Bloomberg says China's decision "is set to spark a global race for alternative sources that may still take a decade to secure sufficient supplies." A spokesman for the German commodities agency is quoted as saying, "We're faced with a gap in rare-earth supplies that cannot be plugged overnight."

Now what: Reuters says Molycorp CEO Mark Smith told a conference today that he doesn't expect a total embargo, but he does believe "we're going to see reductions in the export quotas coming out of China." Because Molycorp is focused on western hemisphere feedstocks, it's natural the stock would move up on the news. Rare Element Resources (AMEX: REE) was also up today, though only 2%.

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Fool analyst Rex Moore owns no companies mentioned here. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.