Bridgmanite: World's most abundant mineral finally named

November 28, 2014 by Bob Yirka report
Meteorite
Credit: NASA

A team of geologists in the U.S. has finally found an analyzable sample of the most abundant mineral in the world allowing them to give it a name: bridgmanite. In their paper published in the journal Science, the team describes how they were able to analyze a sample of the mineral in a meteorite. Thomas Sharp of Arizona State University offers an analysis of the research in the same journal issue.

Earth scientists have known about the (which is made up of high density magnesium iron silicate) for quite some time, it makes up approximately 70 percent of the Earth's which amounts to 38 percent of the Earth's total volume. But it doesn't exist on the planet anywhere else, at least not in samples that have been found. Prior to now, it was referred to as perovskite because according to rules set down by the International Mineralogical Association, a mineral cannot be given a formal name until a specimen has been found that can be examined first hand. The new name is in honor of Percy Bridgman, a pioneer in the use of high pressure experiments to better understand how many geological formations come about.

Because it's not possible to dig down to the lower mantle to obtain a sample of the mineral, scientists have had to look to other sources. Prior research had suggested that it could likely come into existence when two celestial bodies collide—the shock waves could provide the enormous pressure needed. During such a collision, which would involve damage to both colliders, pieces would undoubtedly be flung to the far reaches of space, some of which could make their way to us in the form of a meteorite. In this latest effort, the researchers looked at a likely candidate, a that had fallen to Earth in Australia in 1879.

Scientists had looked at likely candidate meteorites in the past, but the technique (electron diffraction) they used to look for a bit of perovskite wound up causing it to be destroyed. This time, the team used a different, less destructive test—one that involved the use of a micro-focused X-ray beam in conjunction with electronmicroscopy. That allowed them to finally analyze the sample in a way that confirmed the mineral was in fact, perovskite.

The researchers noted that the sample has more sodium and ferric acid than had been expected—and their finding is expected to aid in future geological research efforts, and might even hold clues about what goes on when collide, which in turn could offer more insight into the formation of the universe.

Explore further: Our planet's most abundant mineral now has a name

More information: Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite, Science 28 November 2014: Vol. 346 no. 6213 pp. 1100-1102 DOI: 10.1126/science.1259369

ABSTRACT
Meteorites exposed to high pressures and temperatures during impact-induced shock often contain minerals whose occurrence and stability normally confine them to the deeper portions of Earth's mantle. One exception has been MgSiO3 in the perovskite structure, which is the most abundant solid phase in Earth. Here we report the discovery of this important phase as a mineral in the Tenham L6 chondrite and approved by the International Mineralogical Association (specimen IMA 2014-017). MgSiO3-perovskite is now called bridgmanite. The associated phase assemblage constrains peak shock conditions to ~ 24 gigapascals and 2300 kelvin. The discovery concludes a half century of efforts to find, identify, and characterize a natural specimen of this important mineral.

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3 comments

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dan42day
4 / 5 (4) Nov 28, 2014
I find it interesting that we can be certain that this material makes up 70% of the lower mantle where we have no way of accessing it, yet it is extremely difficult to identify a sample of it in a meteorite that we can hold in our hand and slice and dice at will.
Lex Talonis
4.2 / 5 (5) Nov 28, 2014
@dan42day....

Well, you see it's like being in the Sahara dessert, and being able to calculate the structure of ice, from established principles, like steam and frost etc., and not being able to get to the poles or mountain tops to establish proof, for the calculations.
Torbjorn_Larsson_OM
3.7 / 5 (3) Nov 29, 2014
Yes, the models said there were a stable perovskite structure of MgSiO3, and then they found it. I'm confident the crystal dimensions are a match to the model.

Possibly there are other similar structures if the models are wrong on details. But seeing how hard it was to find a sample it should be the one the models constrain to be stable.

"The discovery concludes a half century of efforts to find, identify, and characterize a natural specimen of this important mineral." [Abstract]

That reminds me that it took about the same amount of time to find the mantle water, they could produce the water-containing mineral (ringwoodite) synthetically, but it wasn't until this spring they found an diamond-protected inclusion of it with the predicted amount of water. [ http://www.scient...f-water/ ]

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