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story & photos by ellen thompson
A geologist who specializes in finding diamonds, but has never found any, came to the Bear Paw Mountains season after season to study the process that carries the valuable gems to the earth's surface.
Though Dr. Carter Hearn's work has never resulted in a sparkly discovery, it does have practical application. He's responsible for much of the work that went into the creation of the U.S. Geological Survey maps of the Bear Paws. The maps have practical purposes for finding other buried treasure, such as water, oil and gas, and for learning about the inner workings of the earth.
Hearn is an East Coast native who came to north-central Montana for the first time in 1955 to work on his doctoral thesis. Since that time, he has spent at least 15 more seasons in the area, and plenty of time exploring the rest of Montana. When in the Bear Paws, he spends his time mapping the mountains and is always looking for "odd" rocks.
Diamonds are found in kimberlites, volcanic rock that comes up from deep in the Earth during an upheaval. They are found afterward in volcanic pipes, what Hearn calls the throat of the volcano. Those pipes are common to the Bear Paws, though none carry diamonds.
"Something happens at great depth that is ripping out rocks along the passage where the rock is going to the surface," Hearn said xploring the region to find out what there is to learn about the earth's deeper regions, information that is available through study of the area.
Hearn's curiosity brought him back to the area this summer, as it has in other summers, even after he retired. He was here in August, still looking for odd rocks.
If those rocks have a specific makeup, they are called kimberlites. They often contain garnet and other green minerals, but are often found in dark black rock - blacker than the usual shale in the area.
"I've gotten a lot of help from the ranchers in looking for these obscure volcanic occurrences because the ranchers always know where there are unusual rocks on their place," Hearn said while visiting the area last month.
Hearn said he's learned a lot from the area. It was where he got his first intensive field experience. But he admitted, "It would be fun" to find a diamond.
Instead, he's found a lifestyle he's enjoyed. Hearn is an avid canoeist, and with his frequent trips to Montana, he's had time to pursue his hobby along with his profession.
"I love being in Montana," Hearn said.
The rest of the year, Hearn lives in the Washington, D.C. area. He splits his time between volunteering for the Smithsonian Museum, where he catalogues rocks found by other geologists, and visiting an office with the U.S. Geological Survey, where he keeps up on projects.
Aside from the presence of kimberlites, the Bear Paw Mountains are unusual for another reason - the range's structure.
"It's a classic area of what's called gravity sliding," Hearn said.
At the base of the range, rising rock causes sheets from the outer layer of the mountains to slough off, where they meet resistance, creating ripples out from the center.
In the 50 years since Hearn first came to north-central Montana, a lot has changed in the world, but not much of the local geology.
"There are a few more landslides and a few rock falls, and that's about it," Hearn said. "Some of the rivers have changed."