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 rare-earth metals producer Molycorp (NYSE: MCP) had a rare down day on Thursday, sinking as much as 12% on extraordinarily high volume.

So what: According to Streetinsider.com, Byron Capital Markets analyst Jon Hykawy opined yesterday that the price of certain rare-earth metals -- lanthanum and cerium -- could fall hard, suggesting a looming risk to Molycorp's profitability. It's tough to tell whether that Wall Street call is the main driver of today's heavy sell-off, but with Rare Element Resources (AMEX: REE) and the Market Vectors Rare Earth/Strategic Metals ETF (NYSE: REMX) also down big, investors certainly seem concerned about something.

Now what: This is obviously one price plunge that isn't worth pouncing on. Even with today's double-digit loss, Molycorp is up more than 300% since its July IPO and still sports an almost unbelievable $4.5 billion market cap. In other words, the stock has a lot more room to fall before it becomes even a reasonable speculation.

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