Museum experts say they're calling the meteorite -- donated by a private collector -- "The Oddball."
"It does not fall into any of the classes of asteroid or meteorites that we know of," museum geologist James Holstein told WBBM Newsradio, Chicago. "So this is truly from a new world in our solar system."
While meteorites are typically black or grey, the museum's example is further confounding experts by being a distinctive shade of green, leading to speculation as to where it might have come from.
"Some scientists are pushing this idea forward that this came from Mercury, but we feel at this point that the evidence is kind of weak. It could be," Holstein said. "We're not going to rule it out, of course, but we feel that it's probably more likely than not from the asteroid belt between Mars and Jupiter."
The public will get a chance to see the "oddball" space rock later this year as part of a planned larger meteorite exhibit, museum officials said.