(FORTUNE Small Business) – Some of these don't look like much," admits Mike Farmer, 31, ushering me into the dining room of his Tucson home and gesturing at the crowded table. Some? They all look like rocks.

Except that they're strangely black and dense. The one I'm holding now resembles a burned meatloaf and weighs as much as an antique Smith-Corona. Farmer came upon it in mid-January while trolling by truck at dawn in the desert of Oman. "I actually thought it was a camel crap," he says. A UCLA scientist, one of many he regularly consults, identified it as a rare meteorite known as a ureilite. Retail value: $40,000.

Farmer is a professional meteorite hunter, one of a handful in the U.S. In 2003, he says, he grossed a half-million dollars, netting $125,000 (he spends $120,000 on travel). If he's not scouring the world's whitest deserts, searching for objects that look out of place, he's chasing a reported fall. He spent two weeks in India last October, at the site of a spectacular shower near the Bay of Bengal, but came away empty-handed when a cyclone flooded the zone under six feet of water. "It was horrible," says Farmer. "People were dying. The meteorites were all lost." He fared better last March in Chicago, scoring from one startled homeowner a two-pound rock, the printer it had pulverized, and the hole it had made in the roof.("I had a carpenter cut it out of the roof for me.") Farmer sold the set to a client for $50,000, having paid $12,000. More often, he sells via eBay or at shows.

Eight years ago Farmer was still in college when he bought his first meteorite at the Tucson Gem Show. "I was so fascinated," he says. Farmer's wife, Melodye, was "apprehensive," she says--"I mean, selling rocks?" She began to soften after Farmer acquired a moon rock in 2000 for $11,700 from a broker in Morocco, sold his share for $280,000, and then bought her a house, a mega-SUV, and a vacation in Tahiti.

Farmer could boost his income if he weren't such a passionate collector. His office display case holds specimens worth $1 million. They are uninsured, but Farmer's not worried. "If anyone breaks in, they'll take my VCR," he says. "Why bother with rocks?"