An analysis of a huge chunk of space rock that fell to Earth in Somalia has revealed materials never before seen in nature.
Two new minerals have been analyzed and named, and a
possible third is currently under consideration by the International
Mineralogical Association.
This discovery could give scientists some important clues as
to the formation of asteroids and meteorites.
The minerals have been named elaiite and elkinstantonite,
and their discovery was announced by planetary geologist Chris Herd of the
University of Alberta in Canada at the Space Exploration Symposium on 21
November.
"Whenever you find a new mineral, it means that the actual geological conditions, the chemistry of the rock, was different than what's been found before," Herd says. "That's what makes this exciting: In this particular meteorite you have two officially described minerals that are new to science."
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Elaliite inclusion in the meteorite. (Chi Ma/Caltech) |
Partially embedded in sand in a limestone-rich valley in
Somalia near the town of El Ali, the rock in question was only recently
identified as a meteorite – a 15.2-ton boulder that happens to be the
ninth-largest space rock ever found on Earth's surface.
It's unclear when it fell from the sky, but locals had named
the rock "Nightfall", memorializing it in folklore, songs, and dance
for at least 5 to 7 generations and using it as an anvil for knife-sharpening.
Prospectors looking for opal in the area in 2019, intrigued
by the strange, pitted rock, struck off some samples and sent them to Herd and
for analysis and classification at the University of Alberta's Meteorite
Collection.
In collaboration with researchers at the University of
California, Los Angeles, and the California Institute of Technology, Herd soon
determined Nightfall was an iron meteorite belonging to the IAB complex, and
officially named it El Ali, after the nearby town.
The iron IAB complex classification contains around 350
meteorites, and they are characterized by, among other things, a predominantly
iron-nickel composition, with inclusions of silicates like tiny raisins in a
fruitcake. They're thought to have formed from impact-induced melting on an
iron asteroid.
To classify the meteorite, Herd and his team needed to study
the chemical composition, and this is when things took a turn. Some of the
inclusions seemed to have an unusual texture and composition, so Herd enlisted
the aid of University of Alberta mineralogist Andrew Locock, who has been
involved in describing other new minerals.
"The very first day he did some analyses, he said, 'You've got at least two new minerals in there'," Herd says. "That was phenomenal. Most of the time it takes a lot more work than that to say there's a new mineral."
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Elkinstantonite in the El Ali meteorite. (Chi Ma/Caltech) |
The two minerals had iron-phosphorus-oxygen compositions.
Elaliite, named after El Ali, has the formula Fe2+8Fe3+(PO4)O8.
Elkinstantonite, named for planetary scientist Lindy Elkins-Tanton of Arizona
State University, has the formula Fe4(PO4)2O. Elkins-Tanton has done a lot of
influential work on how planetary cores and iron meteorites form.
Usually, a new mineral might take a bit longer to identify,
but similar minerals to these two had been synthesized in a laboratory setting
in the 1980s, making them a lot easier to recognize as something new. Now that
they have been found in nature, the two minerals get official classification
and names.
A third potential new mineral is still undergoing the
process of identification and classification. In addition, scientists are
working on a paper describing the formation processes that could produce these
minerals, and what that means for the formation of the El Ali meteorite itself.
"That's my expertise – how you tease out the geologic
processes and the geologic history of the asteroid this rock was once part
of," says Herd. "I never thought I'd be involved in describing brand
new minerals just by virtue of working on a meteorite."
As for Nightfall itself, it was removed from the place it
lay for generations, and taken to Somalia's capital, Mogadishu, where it was
weighed before being seized by the Somalian government. What happened to it
after that is unclear, but Herd said that reports suggested it was moved to
China, where it may sit in the hands of meteorite dealers, who would cut it up
and sell it.
The scientists are trying to track it down, in the hope of
working with meteorite dealers and collectors to obtain more pieces of the rock
and conduct further research.
"There is more material out there; it just needs to get
in the hands of scientists so that we can maybe find some other new
minerals," Herd said to close his presentation.
The discovery was announced at the Space ExplorationSymposium 2022.