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 specialty mineral producer Amcol (NYSE: ACO) fell 10% at the open of trading this morning after it barely missed earnings estimates.

So what: Fourth-quarter revenue grew 6.5%, to $233.7 million, just short of the $236.2 million analysts had expected. Earnings per share were in line with expectations at $0.43 per share.

Now what: The stock sold off sharply at the open, but has climbed back to a small gain as of this writing. The earnings report wasn't all that bad and barely missed expectations, so the beating the stock took early was very overdone. All in all, I wouldn't panic about the drop this morning since the market came to its senses later in the day.

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