Photograph courtesy Chi Ma, Caltech
Published May 19, 2011
Two new minerals that formed during the birth of our solar system have been found inside meteorites, new research shows.
The new discoveries—krotite and wassonite—are particularly exciting for scientists, who have found only about 60 minerals that can be traced to the solar system's beginnings 4.5 billion years ago.
"These 60 primary minerals plus a dozen ... presolar minerals are the beginning of mineral evolution in our solar system," said Chi Ma, a mineralogist at the California Institute of Technology who led the study on krotite.
"They are our ... starting materials, which evolve under different physical, chemical, and biological conditions until now—on our own planet we have about 4,500 minerals."
Krotite Found in "Cracked Egg" Meteorite
Krotite, named for pioneering cosmochemist Alexander Krot of the University of Hawaii, was discovered in a meteorite collected about eight years ago in North Africa.
While recently examining the meteorite, scientists spotted an odd material that looked like a cracked egg and was about the size of a grain of rice.
Laboratory analyses revealed that krotite contains a type of calcium aluminum oxide (CaAl2O4) that forms only when there's a combination of low pressure and high temperatures above 2,700 degrees Fahrenheit (1,500 degrees Celsius). These were also the conditions during the dawn of the solar system—which is why the minerals' discoveries are so interesting to scientists.
The same material is well known in the field of synthetic materials science, and is sometimes used in concrete. "But this is the first time [it] was found in nature," said Ma, who describes krotite in the May issue of American Mineralogist.
(Also see "Oldest Rocks on Earth Discovered?")
Antarctic Meteorite Reveals Wassonite
Wassonite—named for John Wasson, a pioneer in meteorite mineralogy at the University of California, Los Angeles—was found in a meteorite known as Yamato 691.
Several years ago, UCLA scientists noticed strange, microscopic crystals inside the Yamato meteorite, which was collected in Antarctica 42 years ago, said Keiko Nakamura-Messenger, a mineralogist at NASA's Johnson Space Center in Houston, Texas.
But the crystals, which measured only 50 by 450 nanometers—about a hundredth the width of a human hair—were too tiny to analyze until recently.
(Related pictures: "Best Micro-Photos of 2010.")
Using an instrument called a focused ion beam, a team led by Nakamura-Messenger prized the crystals out of the rock.
The team then analyzed the crystals' chemical structures, which revealed that they were composed of just two elements, titanium and sulfur.
Those elements occurred in a 1:1 ratio—an extremely simple formula for a never before seen mineral.
The crystal structure itself, however, is a bit more complex, said Nakamura-Messenger, whose paper on wassonite is pending publication. "You'd expect a cube. But it isn't." Rather, "it has an elongated rhombohedral structure."
In other words, the crystal resembles an office tower that's been shoved slightly out of plumb.
New Minerals Give Window Into Solar System Birth
The newfound minerals may give scientists clues for how minerals formed at the dawn of time.
Astronomers believe that the solar system began as a hot cloud of gas called the solar nebula. As the temperature dropped in the cloud, dust crystals eventually condensed.
This means high-temperature minerals such as krotite were among the first to form.
"There's not many of them," said Caltech's Ma. "Around 30. This was one of the first solids formed in the solar nebula. That's what makes it so exciting. Those minerals tell us what's going on at the very beginning of the solar system."
Because of krotite's relationship to known human-made substances, the conditions under which it forms are already known.
Wassonite, on the other hand, will require more study.
"By studying this mineral, we can understand a little bit more about the solar system," NASA's Nakamura-Messenger said. "Four-and-a-half billion years ago, there was a region that had the exact conditions to make this mineral."
What's more, this may not be the only new mineral in the Yamato 691 meteorite.
"The wassonite was surrounded by a couple of other unknown mineral[s]," Nakamura-Messenger said.
Likewise, another new mineral, called brearleyite, has been identified next to krotite, Caltech's Ma added—details to be revealed in August in American Mineralogist.
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