Contest open for name for big boulder dug up at O'Hare International Airport

The Chicago Department of Aviation is holding a contest to name a boulder found under O'Hare International Airport during construction work.

The 50-ton boulder was found about 30 feet below the surface of the airfield at O'Hare during excavation of the South Detention Basin, a stormwater management facility. The work is part of the ORDNext project — the largest terminal expansion in the history of the airport.

The boulder is about 11.5 feet wide, 8 feet deep, and 7.5 feet tall. A geologist working for the ORDNext project said it was made of dolostone, a sedimentary carbonate rock made up mostly of the mineral dolomite, or calcium magnesium carbonate — chemical formula CaMg(CO₃)₂.

Dolostone is related to limestone, and can form as groundwater rich in magnesium passes through limestone or lime mud and replaces the calcium ions in the limestone with magnesium, the department explained.

The public may propose names for the big boulder with an online form. Aviation Commissioner Mike McMurray said so far, staffers have been calling it the "O'Hare bean" internally, but "a rock of this magnitude deserves a name of its own."

After three weeks, the department will review the entries and select five finalists for a public vote.

The winning name will not be etched in stone, but it will appear in an exhibit at the airport and on the social media channels at O'Hare.