MUSEUM CAMPUS — The Field Museum's newest meteorite is the first of its kind discovered on Earth.
The small rock cluster, which is green and has a crystalline texture, is known officially as "Northwest Africa 7325." It was found in Morocco in 2012, and researchers know little else about it.
"This is a new type of meteorite that we don't know about yet," said James Holstein, who manages meteorites and physical geology at the museum. "We don't know where it came from."
Holstein said there are about 45,000 known meteorites, which scientists sort into five different classes.
This meteorite doesn't fit into any of them.
"It doesn't match up to any other meteorites. It's similar [to some], but not an exact match."
At first glance, Holstein said, the greenish rock — which is shattered into several pieces, the largest about the size of a D battery — looks like it could come from Earth. But oxygen isotope analysis tells scientists it's definitely not terrestrial.
Researchers estimate the meteorite came from a planet formed 4.5 billion years ago.
While some have speculated that planet was Mercury, Holstein said evidence of that is weak. In all probability, he said, the meteorite came from an asteroid somewhere between Mars and Jupiter.
The meteorite arrived at the Field Museum on Wednesday and will be kept behind the scenes until later this year as researchers continue to study the mystery rock.
"This rock comes from a planetary body that has not been sampled before," said associate curator Phillip Heck. "Its study will enhance our picture of the diversity of planets in our solar system."
Holstein said he hoped the green meteorite would join the Field Museum's more than 10,000 meteorite specimens by late summer.