You may have a crazy Aunt Gertrude or Uncle Cyrus who, for no apparent reason, is awfully hard to get along with. And if you don't have such a person in your lineage, there's always the market, which is exhibiting frequent signs of irrationality and dementia these days.

That likely would be the assessment from the management of copper, molybdenum, and gold producer Freeport-McMoRan (NYSE: FCX), which Wednesday blew the doors off its March-ended quarterly earnings -- including clobbering analysts' expectations. Its reward was a yawn from the Uncle Cyrus market. That crazy Uncle Cyrus.

For the quarter, Freeport earned $1.12 billion, or $2.64 a share, more than double the $476 million in the same quarter a year ago. (The dart-throwers apparently had been looking for about $2.12 a share.) While a portion of the increase was tied to Freeport's March 2007 acquisition of Phelps Dodge, a copper producer about twice its size, the lion's share related to the hike in copper prices from less than $3 as recently as late last year to a current level near $4.

While some of the market's petulance may relate to increasing development costs at the company's Tenke Fungurume copper project in the Democratic Republic of Congo, the overriding question for Freeport clearly involves where those copper prices may be headed from here. Obviously, demand is weak in the U.S., as the housing and automobile markets have retreated.

But for the most part, developing nations like China have more than taken up the slack. In fact, as Freeport CEO Richard Adkerson observed during the company's conference call, the U.S. plays a relatively minor part in the global demand for copper.

Freeport clearly is in the same league with such other big mining companies as BHP Billiton (NYSE: BHP), Rio Tinto (NYSE: RTP), Vale (NYSE: RIO), and Southern Copper (NYSE: PCU). All are trying to satisfy the voracious appetite of the developing world for everything from iron ore to aluminum to copper.

So with copper prices up from less than a dollar a pound just five years ago, and with global demand unlikely to slide for anything approaching an extended period, I'm willing to bet my bucks on the Phoenix-based company with low P/E and PEG ratios and oodles of high-quality, geographically diverse reserves of desired metals.

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In a past life, Fool contributor David Lee Smith climbed around Freeport's Sierrita copper mine, south of Tucson. He doesn't own shares in any of the companies mentioned, but he does welcome your comments. The Fool has a golden disclosure policy.