#bridgmanite

[scienza-magia]

La dinamica interna della Terra scritta nei diamanti super-profondi

Com’è fatto il centro della terra? Se è raro e super profondo a dirlo è un diamante. Pubblicato su «PNAS» lo studio del team guidato da Chiara Anzolini del Dipartimento di Geoscienze dell’Università di Padova che spiega la composizione chimica e mineralogica dell’interno della Terra partendo da una microscopica sequenza di minerali decifrata all’interno di un diamante Oltre 50 anni di studi sperimentali finalizzati a comprendere di cosa sia fatto l’interno della Terra hanno portato alla scoperta di importanti minerali (wadsleyite, ringwoodite, bridgmanite e ferropericlasio) considerati essere rappresentativi della composizione mineralogica del pianeta a profondità maggiori di 400 km. Simulazioni in laboratorio delle condizioni primordiali di pressione (10.000 atmosfere ogni 30 km di profondità) e temperatura (3 °C ogni 100 metri) hanno dimostrato che questi minerali furono tra i primi a formarsi man mano che il nucleo terrestre – una lega di Ferro e Nichel – solidificava a seguito del raffreddamento della palla di magma che costituiva il nostro pianeta più di 4.5 miliardi di anni fa. Eppure, la composizione chimica e mineralogica dell’interno della Terra risulta ancora poco nota, perché le osservazioni dirette – essendo piuttosto complesse – non sono numerose. Read the full article

[arko006-blog]

Researchers find UK's Crown Jewels and Smithsonian's Hope diamonds came from

Researchers find UK’s Crown Jewels and Smithsonian’s Hope diamonds came from

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FP TrendingJun 26, 2020 09:49:40 IST

Researchers have now found evidence that some of the world’s most impressive diamonds originated much deeper in the Earth’s mantle than earlier thought.

According to a report in Phys.org, this means that the Smithsonian’s famous Hope diamond may actually have originated from more than three times deeper in the Earth than other diamonds.

The report…

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[earthstory]

Deep diamond brings us unique sample of a common mantle mineral

In the extreme heat and pressure that reign in the planet's mantle common chemical compositions that take on the form of familiar minerals such as olivine (see http://bit.ly/2AbnsV4) in surface or shallow crustal environments take on different forms, which have been experimentally produced by that branch of the Earth sciences that I nickname rock squishers but are never seen at the surface since they would change structure into different minerals or weather chemically away into something different (minerals like diamond which survive outside their conditions are known as metastable). One of these is the calcium silicate mineral Perovskite (the 4th most common mineral forming the planet), which has been found as an inclusion in a diamond for the first time and is thought to be one of the most common minerals down there in the depths.

There are two discontinuities in the shallow mantle, visible on seismic maps as changes in the velocity of the propagating waves, one around 440km down and the other at 660. Both of these are thought to reflect changes in mineral phase as atoms rearrange themselves into structures and geometrical configurations more suitable to their surroundings. Perovskite comes from some 700km down, and was found included in a deep diamond (most form some 150-200km down) from the historic Cullinan mine in South Africa (where the biggest diamond ever found was mined, some of whose remnants grace the British crown jewels).

Analysis of the inclusion revealed an isotopic component (isotopes are different versions of the same element, with different atomic weights due to extra neutrons in the structure) from recycled oceanic crust that went down into the mantle after a long gone subduction event. This proves that sinking slabs can indeed pass through the above mentioned discontinuities, which has been a matter of debate, and confirms expectations that much slab material might turn into Perovskite and be recycled in the mantle because of the large amount of calcium that such rocks contain, both from the marine sediments layered above the basalt and the hydrothermal calcite precipitated in its bubbles.

The same team discovered the 5th most abundant mineral on Earth (called Ringwoodite ) in another diamond back in 2014, incidentally proving that a vast amount of water was sloshing around in the mantle ( see http://bit.ly/1M1SPh0 and http://bit.ly/2G0Nzhg)

Loz

Image credit: Nester Korolev/University of British Columbia

http://bit.ly/2FUx1at http://bit.ly/2HNjgLm http://bit.ly/2FSKm3f

Original paper, paywall access: http://go.nature.com/2FVkWCd

[shinden9]

Despite being the most abundant mineral in planet Earth, Bridgmanite did not have a name until the middle of this year. This is because, despite scientists knowing it exists, knowing its chemical makeup, and knowing how it forms, they could not obtain a specimen, as it exists in the Earth's lower mantle. I guess you could say those scientists... really craved that mineral.

[worldofchemicals]

The most abundant mineral on earth that has remained nameless until now will be called Bridgmanite. After a team of American geologists were able to extract a sample large enough to analyze from a meteorite, Bridgmanite was named officially.

Until 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 honour of Percy Bridgman, a pioneer in the use of high pressure experiments to better understand how many geological formations come about.

Bridgmanite makes up about 70 per cent of the earth’s lower mantle and 38 per cent of the total volume of earth. It is made up of high-density magnesium iron silicate.

The lower mantle which starts at 670km under the crust is difficult to reach for samples. The researchers looked at a meteorite that had fallen inside Australia in 1879 as a likely candidate for samples, and found what they were looking for.

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 electron microscopy. The researchers noted that the sample had more sodium and ferric acid than had been expected.

Their discovery is expected to aid future geological research and could offer clues about what goes on when celestial bodies collide, and potentially also about the formation of the universe.

[newsagram]

VIDEO: You'll Never Guess What 30% Of The Earth Is Made Of - DNews

VIDEO: You’ll Never Guess What 30% Of The Earth Is Made Of – DNews

In 1879, the Earth’s most abundant mineral was discovered, but it was only just recently named! What took so long?

(more…)

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[kqedscience]

Earth's Most Common Mineral Is Bagged and Tagged: Meet Bridgmanite

"Giving names to newly discovered minerals is a sideshow in the carnival of science, like one of those booths where you toss a ball in a cup to win a stuffed animal. By that analogy, a team of scientists has won the giant stuffed panda, and the achievement was enough to rate a paper in the prestigious journal Science last week. They successfully identified the commonest mineral that makes up the Earth, and gave it the name of bridgmanite."

Learn more about the person who inspired the mineral's name from Andrew Alden at KQED Science.

[renerdssanceman]

Today I learned about the most common mineral on Earth, and how it didn't have a name until recently because we had never been able to study a sample of it in its natural state.

The mineral is believed to exist in massive quantities in the Earth's lower mantle, and is an extremely dense version of magnesium iron silicate. It comprises a staggering 38% of the Earth's volume, but a vanishingly small amount has been found at the surface because it is only stable at pressures found ~650km underground.

Scientists found a sample of it from a meteorite that hit Australia in the 19th century; microscopic pieces of the mineral remained after two asteroids collided and one fell to Earth. It remained stable due to being exposed to the cold vacuum of space.

The mineral is now called Bridgmanite after Percy Bridgman, an American Nobel laureate physicist who pioneered techniques for studying minerals under extraordinarily high pressures.