Aluminum is highly durable and very resistant to corrosion. Unfortunately, the same cannot be said of Alcoa (NYSE:AA) or its stock. Things aren't looking much better today, as this old-school aluminum company cut third-quarter guidance by a pretty considerable amount.

Instead of the mean analyst estimate of $0.43 per share, management is now looking for third-quarter earnings to come in around $0.27 to $0.31. That's a steep drop in its own right, made all the worse by noticing that the estimate for the third quarter stood at $0.50 just a few months back.

Fools with some investing experience in metals might already suspect what nailed Alcoa this quarter, but let's take a closer look. Remember, the company is sandwiched between a fluctuating end-product price that it can't control and fluctuating input prices that it also can't control. During the quarter, the company reported that the price of aluminum as measured by the price on the London Metal Exchange dropped $80/ton and that it saw a further reduction of $40/ton in the premium for delivering aluminum to the Midwest.

That's not good, but it gets even worse. Energy prices spiked in the third quarter as natural gas climbed from a range of roughly $7.50 to $8.50 in the second quarter to as much as $14.00 in the third quarter. In fact, if you look at a chart of the December NYMEX natural gas contract, you see an almost unbroken upward line starting in mid-July. What's more, it's not as though the company has seen any real breaks on electricity or chemical prices, either.

Since companies are often hesitant to dish out details about their hedging and their contracts, it can be tough to project exactly what sort of impact this will have across the sector. Canada's Alcan (NYSE:AL) could be in for a rough quarter as well, while it's possible that increased production will outstrip increased costs for China's Aluminum Company of China (NYSE:ACH), but I just can't say for sure one way or the other. In general, though, investors who hold metal stocks with a lot of exposure to energy prices might want to prepare themselves for a tough quarter.

For more metallurgic Foolishness, bang around in here:

Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).