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 coal producer Alpha Natural Resources (NYSE: ANR) woke up on the wrong side of the bed to start the week and fell 10% in trading today.

So what: There's no one news story hurting Alpha Natural today, instead, it's a range of things investors are selling on to start the week. First, the energy sector has been hit hard today because of concerns Europe's debt problems are far from over. There's also pessimism hanging over coal stocks after Goldman Sachs downgraded the sector from attractive to neutral last week. To top it off, last week a $200 million settlement over Massey's mine accident last year has hurt the company.

Now what: With stocks selling off across the board, Alpha Natural is being hit hard because it was especially weak after all of the bad news last week. Before jumping into coal stocks, I would look at energy's trend away from coal and toward natural gas and a variety of renewable energy sources as a big caution flag. I would much rather be in a growing part of the energy sector than in coal, which is very slowly going out of favor.

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