Joseph Mengel made the suggestion based on his avid reading, knowledge of Lake Superior and simple curiosity: The fibers in taconite tailings, he said, look an awful lot like those causing stomach cancer in Japan.

Mengel's thought ended up playing a key role in the historic dispute involving the Reserve Mining Co. over its dumping of taconite tailings into Lake Superior. That 1970s case raised the first questions -- many of them still unanswered -- about the health risks of asbestos-related mineral fibers in the low-grade iron ore.

"If you look at the chain of causation in that case, Joe's discovery was one of the very critical junctures," said Grant Merritt, executive director of the Minnesota Pollution Control Agency from 1971 to 1975.

Mengel, a former University of Wisconsin-Superior geology professor, died July 23. The Eden Prairie resident was 79.

Born in Knoxville, Tenn., Mengel joined the faculty of UW-Superior in 1961. He studied ancient iron-bearing rocks and taught courses about the geology of the Lake Superior region.

One day in 1972, Mengel accidentally attended the wrong convention and found himself in a conversation with Arlene Lehto, then president of the Save Lake Superior Association.

"I told her that I had just read about stomach cancer in Japan which was cause by sharp, asbestos-like fibers used to polish rice," Mengel later wrote in a short autobiography. The accompanying photomicrograph "showed sharp micro fibers which looked to be strikingly similar to those which I had seen for years in Lake Superior."

That thought quickly traveled from the Duluth hotel to Merritt's Twin Cities office. The agency hired a geologist to further study the similarity.

Mengel cared deeply about the lake, but was never attempting to "take down" the mining company, friends said. He demonstrated this by suggesting that Reserve Mining's waste was not the only source of asbestos-like fibers in the lake. By plotting the location and direction of glacial striations, he proved that some prehistoric sediments contained the fibers.

"This discovery helped to bring a measure of balance to the charges being made by the government," he wrote. "It was a neat case of forensic geology providing a context for legal/political actions."

David Parr, a friend and former UW-Superior colleague, called Mengel a skilled thinker and voracious reader on a broad set of subjects: science, spirituality, politics, history. The book he was reading just before his death was "The Social Animal," by New York Times columnist David Brooks. Mengel donated 2,500 books to UW-Superior.

Mengel believed that "you will never know enough," Parr said. "However much you know, there is still so much more to learn."

Frustrated by the lack of detail in newspaper obituaries, Mengel wrote his own. "He was a geologist," he wrote, "a lifelong student/teacher, crusader against ignorance inside himself and elsewhere." The short piece concluded with a reference to engineer, author and futurist Buckminster Fuller: "Joe rejoined the Spaceship Earth geochemical cycle through cremation."

No services were held, at his request, daughter Maria Mengel said. But a small group of family and friends gathered anyway, placing his belongings on several tall tables at the Cremation Society of Minnesota.

On one, photos. On another, his master's and Ph.D. degrees, both from the University of Wisconsin-Madison. On a third, his compass and hammer.

Mengel's survivors include his daughters, Maria of Edina and Melissa of Littleton, Colo. His wife, Mary, preceded him in death.

Staff writer David Shaffer's articles on the Reserve Mining Co. case contributed to this report. Jenna Ross • 612-673-7168