When we Motley Fool writers dare to suggest that today's prices for commodity metals like nickel, zinc, and aluminum will ultimately fall, we usually receive a reliable deluge of "How dare you?!" emails. People will point to China and India, or underinvestment in production assets, or still other points of reference, but few seem willing to accept that cycles have tops and bottoms.

Well, ponder this -- the CEO of Alcan (NYSE:AL), one of the largest aluminum producers in the world, says that we're at the top of the cycle. On more than one occasion, usually when asked about buying any of Falconbridge's (NYSE:FAL) aluminum assets, Dick Evans has gone on the record with such statements. I'm the first to admit, and I'll suspect Mr. Evans agrees, that nobody knows whether we'll enjoy a long plateau at the top, or when the downswing will begin. Nevertheless, I wouldn't get too comfortable with the idea that basic metal prices will continue to rise indefinitely.

By the same token, that doesn't mean current results aren't pretty good. Alcan posted 17% revenue growth, and growth margins improved by more than three percentage points. While there are a few different ways to look at earnings growth (continuing operations, operating earnings, and so on), all of them show pronounced growth from last year.

That growth is still primarily fueled by strong pricing and internal operating improvements. Total volume increased just 2.4% this quarter (with ingot volume a little higher), but ingot price realizations were up by one-third.

Unlike Alcoa (NYSE:AA), Alcan sounded a bit more optimistic about near-term guidance. Though Alcoa is a little cheaper today, I think there's good reason for the discount, and I'd probably be more inclined to like Alcan right now. By the same token, owning such cyclical commodity companies is an invitation to headaches. Foolish investors may wish to seek investment ideas with more enduring competitive advantages.

For more metal-minded Foolishness:

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