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 miner Cliffs Natural Resources, Inc. (NYSE:CLF) jumped as much as 13% today after an activist investor bought a stake.

So what: Casablanca Capital announced it has taken a 5.2% stake in the company and called for change across the board. In a letter to management, Casablanca said it wants to spin off Bloom Lake and other international assets, convert U.S. assets into an MLP, and a number of cost-cutting measures and divestitures as well.  

Now what: Cliffs Natural has swung back to a profit recently and it's probably true that management could do more to save money and unlock value. But I'll also point out that the MLP spinoff is a very popular and predictable thing for a hedge fund to ask for right now with questionable value-add for shareholders. I don't think this alone is a reason to buy Cliffs and the assumption that shares could be worth $53 assumes that the separate parts are worth more than the whole, which may or may not be true.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.