ARLINGTON, MINN. – Farmer Bruce Lilienthal has a favorite saying: "Rocks are a crop we always harvest, but never plant."

He shared that joke Wednesday as he sat in the kitchen of his Sibley County farmhouse, explaining that each spring before planting, he gathers large rocks that frost has pushed to the surface before they can damage his tillage equipment.

Lilienthal saves unique rocks in a pile near his driveway, but one in particular is especially unusual.

It's a rare meteorite, at 4.6 billion years old — roughly the same age as our sun — and one of only nine or 10 that have been confirmed in Minnesota since European settlement.

"We've done enough tests to be sure it's a meteorite," said University of Minnesota earth sciences Prof. Calvin Alexander. "It is not part of the Earth. It fell out of the sky. It's an iron meteorite that almost certainly was part of an asteroid."

It's also very similar to a smaller meteorite discovered in 1894 about 3 miles from Lilienthal's farm, which is near Arlington, about 65 miles southwest of the Twin Cities.

On Wednesday, Lilienthal's meteorite sat displayed in the center of their kitchen table, looking like a severely overcooked pizza the size of a dinner platter.

Its charred exterior testified to its fiery descent into Earth's atmosphere, and its blotchy rust marks showed the weathering of decades — if not centuries — that it remained underground, inching its way to the surface.

Lilienthal, who raises corn, soybeans and beef cattle on about 2,000 acres, said he first spotted the rock half-buried in one of his fields in the spring of 2011. When he reached down to remove it, he was amazed by how heavy it was for its size. It's about 16 inches long, a foot wide and 2 inches thick, but it weighs 33 pounds — four times more than a typical rock would.

It also had a metallic clang, similar to that of an anvil, when tapped against other rocks.

Searching for answers

Lilienthal lugged it to the driveway, where it took its place in the pile of unusual rocks. But over time, curiosity got the better of Lilienthal's wife, Nelva, who ran across photos of meteorites in articles and on websites, and wondered if that might explain their unusual discovery.

The couple sought an explanation recently at the University of Minnesota, and their search led to Alexander, who is also the university's curator of meteorites.

When they brought the rock to his office on the St. Paul campus, his eyes lit up, Nelva said.

"He was kind of shaking, he was so excited," she said.

Alexander estimates that he has looked at 5,000 rocks that people have brought him over the past 40 years, thinking they might be meteorites.

"We affectionately refer to them as meteor-wrongs," he said.

He has confirmed two meteorites from other states, Alexander said, but this was the first new meteorite he's ever seen from Minnesota. It contains more than 90 percent iron and about 8 percent nickel, with a unique crystalline pattern found only in meteorites.

Clues from space

Alexander said small meteorites fall to Earth with some frequency, but usually are too small to find. The rocks are of great interest to collectors and scientists, he said. "Meteorites are our major clues to how the solar system formed," Alexander said. "A huge amount of what we know about the basic geochemistry of the Earth comes from the analysis of meteorites."

The Lilienthals said they will bring the rock to the university again for more research, including a series of photos that may help Alexander and others determine whether it's related to the 19-pound meteorite discovered in the Arlington area 120 years ago.

Beyond that, the couple said they haven't decided what to do with their discovery.

"Right now, it's just the center of conversation," said Bruce Lilienthal. "Maybe we'll sell it or keep it as a family heirloom — unless we find a bigger one."

Tom Meersman • 612-673-7388