CHICAGO -- Ron Pitelka was 23 when he took his first boulder home from work.

Pitelka was on a construction site in Chicago’s southwest suburbs when workers dug up an egg-shaped limestone rock about 5 feet wide. He’d just gotten his first dump truck, which he used to cart the 10,000-pound boulder away.

Over the past two decades, the 45-year-old Local 150 excavator operator says he has amassed a collection of several hundred rocks. Some are at his mom’s place in New Lenox, while a smaller subset — around a hundred of them, he says — are at his house in Homer Glen, about 45 minutes southwest of downtown Chicago. He’s got them lined up on the side of his house and in his driveway, and he’s sure his neighbors hate him for it.

But none of Pitelka’s rocks are as large as the one he helped unearth from under the airfield at O’Hare International Airport this summer with his Caterpillar 352 excavator.

In June, Pitelka was on the job for Walsh Construction, working on an early-stage project for O’Hare’s multibillion-dollar terminal modernization project when he, together with bulldozer operator Matt Tracy, dug up a boulder weighing 50 tons.

Chicago Department of Aviation project manager Cortney Harris said the rock was discovered while the construction crew was excavating dirt from one of the airport’s stormwater detention basins in order to move it to another — an effort that’s part of an $8.8 billion terminal modernization project. The boulder was found about 30 feet underground.

After Pitelka and Tracy dug the rock up, the Aviation Department had it examined by a professional geologist working on the terminal expansion project. The geologist identified the rock as a dolostone, a sedimentary carbonate rock closely related to limestone.

Dolostone forms most of the bedrock of Illinois and was designated the official state rock of Illinois several years ago after a campaign by a group of suburban elementary schoolers.

The Aviation Department has launched a naming contest for the rock and is soliciting submissions from the public. Early name proposals — of which the city has received more than 2,300 — have included Da Layover, Jean Baptiste Point du Pébble, Ferris Boulder and The BaRock Obama Presidential Memorial Airport Boulder, according to CDA spokesperson Kevin Bargnes. Aviation Department staff will choose finalists, and the final choice will be made by public vote.

Pitelka, who says he found out about the naming contest after his neighbor saw it on Channel 7, is thrilled.

Often, he says, contractors ask construction workers to bury boulders or break them up into little pieces — it’s cheaper, he says, than moving them. “It makes me sick to my stomach,” Pitelka said, recalling a particularly beautiful set of blue granite boulders in Plainfield that ended up buried under a residential job site.

The rock material that makes up the O’Hare boulder is likely more than 400 million years old, said Pat McLaughlin, principal research scientist with the Illinois State Geological Survey.

Illinois dolostone formed when the Chicago area “was in the tropics,” McLaughlin said. “There was a shallow tropical sea, and there were all kinds of little critters living in that sea,” he explained. Some of the critters secreted seashells, which accumulated on the sea floor before turning into limestone, and finally into dolostone, McLaughlin said.

“Then the glaciers came in and kind of plucked out big chunks of that rock and moved them around, and that’s where the boulder came from,” he said.

That means the boulder likely became the boulder it is today, in its current shape, size and former location at O’Hare, somewhere around 12,000 to 15,000 years ago.

Clara Blättler, an associate professor in the geophysical sciences department at the University of Chicago, said the rock’s age could be pinpointed by observing it for fossils. The experts agreed the boulder’s size, while not unheard of, is notable for the Chicago area.

The rock is now on public display, having been moved to the airport’s Multi-Modal Facility — home to airport rental car operations, a people mover stop and Metra and Pace connections — at 10255 W. Zemke Boulevard.

Pitelka’s dad and uncle were both excavating contractors, and he says he started running excavators himself when he was 6 years old. “Back in the ’80s, kids could go to work with their dads on construction sites,” he explained. His interest in boulders themselves also started early.

As a kid, he loved playing on a couple boulders his dad had placed outside the family home. As an adult, he still finds joy in the endeavor of digging stuff up.

A lot of excavators, he says, dream of one day digging up a dinosaur. As for himself, he’d love to find a meteorite.

“It’s a very serious job, and requires a lot of skill and a lot of focus, and it can be stressful,” Pitelka said of excavating work. “But it can also be really, really fun.”

Chicagoans still have a little over a week to submit rock names to the city. Pitelka, personally, doesn’t think the rock should be named after a celebrity or given a moniker with political baggage.

Pitelka would simply name it “Geo,” as in geological. “I think it’s very appropriate for a boulder,” he said.

He says he appreciates Geo’s permanence.

“Long after I’m gone, that boulder will still be there,” he said.

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