Meteorites play a role in Minnesota's mineral wealth. And some meteorites are more valuable than gold. The problem is finding them, according to University of Minnesota earth sciences professor and meteorite expert Calvin Alexander.
"Something on the order of 10 fist-sized meteorites or larger hit Minnesota every year," Alexander said.
If you find the rare kind -- pieces of space rock from, say, the moon or Mars, your ship has come in.
Rare meteorites fetch prices much higher than gold; in some cases 20 times higher.
"There are a group of very rich people who like to buy meteorites, just to have them so nobody else has them," said Alexander.
But Minnesota is not a lucrative state for meteorite hunters, because "there's just lots and lots of rocks out there."
Calvin Alexander, 68, is a tall, white-haired native of Oklahoma. He's been a professor at the University of Minnesota since 1973.
Alexander's research includes the study of moon rocks, and he's been on a few meteorite hunts.
"Unfortunately, none of them have been successful."
He frequently gets calls from hopeful people who want him to look at a rock they've found.
"On the order of 10,000 people have probably walked in over the last 40 years, and four of them have had meteorites," he said.
And Alexander says two of those four were found someplace else, not in Minnesota.
The problem with meteorite hunting in Minnesota is that the state's landscape and geology are littered with rocks that make meteorite hunting a fool's errand, with one exception -- the Red River Valley, in the northwestern part of the state.
"It's perfectly flat land with no rocks in it."
That's where the Fisher meteorite, one of the state's most famous, was found back in 1894.
Another famous Minnesota meteorite was found in Anoka, back in the 1960s, when a contractor digging a utility hole in a backyard clanged into a bowling ball-sized rock.
Alexander said the homeowner kept the rock, but didn't do anything about it.
"It sat on his porch for 26 years," said Alexander. "And finally his wife told him, 'find out what the blankety-blank thing is, or get it off my porch.'"
He did, and it was a meteorite. It's now in the meteorite collection at the U of M.
Meteorites crashed into the news in late April, when observers said a car-sized space rock crashed into an area of California that in 1849 was the scene of that state's gold rush.
The event set off a rush of meteorite hunters and reporters to the scene. There were photos of adults and children scooping up bottle cap sized pieces of the meteorite.
With visions of dollar signs before them, the meteorite hunters advised the residents to wrap the pieces in foil to protect them from disintegrating and place them in a safe deposit box.
Scientific interest in meteorites languished for most of human history with the view that rocks could not fall out of the sky. The exceptions, Alexander notes, were the Chinese and the Romans who recognized the existence of celestial objects hitting the planet.
The world's collection of meteorites more than doubled due to soil erosion that occurred in the Great Plains in the Dust Bowl era of the 1930s, according to Alexander. Relentless winds carrying away soil particles revealed space rocks that had fallen to earth over the years.
By the 1960s, when Alexander was doing his doctoral dissertation on meteorites, scientists were increasingly interested in the forces that created our solar system. It was a puzzle that could be solved in part by more careful examination of the composition of meteorites; the leftovers, if you will, of the formation of the universe.
The explosion in meteorite prices has put the rocks out of reach for most scientists. Many of the meteorites used for research, Alexander said, come from the so-called blue ice field of Antactica -- which is actually a desert -- where receeding ice reveals meteorites that fell to earth long ago.
Countries including the United States have placed Antarctica off limits to for-profit meteorite hunters, according to Alexander.
That's not the case with the sandless deserts of north Africa, which is another meteorite-rich area of the planet.
Alexander said meteorites have several characteristics that distinguish them from ordinary rocks.
"They look kind of like -- when you look on the inside of them -- like low-grade concrete," he said. "They have this black fusion crust."
That black crust forms when the space rock hits the earth's atmosphere at thousands of miles an hour. The friction bakes the surface of the meteorite.
A distinctive feature of meteorites, not readily detectable to the eyeball, is a fairly high nickel content.
And that brings us to a geological debate about Minnesota's mineral wealth: Where did the nickel deposits in the northeastern part of the state, which are increasingly coveted by mining companies, come from?
Geologists generally agree on part of the answer -- that a huge meteorite struck about 1.8 billion years ago in an area that is now Sudbury, Ontario.
Alexander says that meteorite was so big and powerful that it punched through the earth's crust, and a large volume of nickel-rich magma bubbled up, leaving deposits in what is now northeastern Minnesota.
But Alexander also believes the splatter from that disintegrating nickel-rich meteorite accounts for a portion of the deposits.
"I'm a space cadet from way back. I think they're probably mining at least some fraction of asteroidal nickel."