An elusive crystal, predicted many decades ago, is found trapped in a DIAMOND more than 410 feet below the Earth’s surface

  • The high-pressure form of calcium silicate perovskite was predicted in 1967
  • However, it was never seen in the wild because it is unpredictable at ambient conditions.
  • Experts from the University of Nevada discovered a specimen in a Botswana diamond.
  • The structure was characterized by them and it received the official name of ‘davemaoite.










The discovery of a rare crystal in a deep-Earth diamond has brought to light a long-held prediction.  

High-pressure calcium silicate perovskite — a mineral predicted in 1967, but never before seen in nature — was found in a diamond from the lower mantle.

Researchers led from the University of Nevada used synchrotron x-ray diffraction to characterise the crystalline compound, which they have called ‘davemaoite’. 

Based on their results, davemaoite has now been confirmed as a new mineral by the International Mineralogical Association. 

The choice of name honours the work of the eminent Chinese-American geophysicist Ho-Kwang ‘Dave’ Mao in the field of deep-mantle petrology.

The diamond with the davemaoite inclusion was formed more than 410 miles (660 km) below the Earth’s surface, and was unearthed in the Orapa mine in Botswana.

High-pressure calcium silicate perovskite — an elusive mineral predicted in 1967, but never before seen in nature — has been found in a diamond from the lower mantle (pictured)

High-pressure calcium silicate perovskite — an elusive mineral predicted in 1967, but never before seen in nature — has been found in a diamond from the lower mantle (pictured)

Experts led from the University of Nevada used synchrotron x-ray diffraction on the diamond (pictured) to characterise the crystalline compound, which they have called 'davemaoite'

Experts led from the University of Nevada used synchrotron x-ray diffraction on the diamond (pictured) to characterise the crystalline compound, which they have called ‘davemaoite’

ACCEPT NO IMITATION

Minerals can only be confirmed and assigned a proper name after being discovered existing in nature.

This is why davemaoite has only just been approved by the International Mineralogical Association, despite the fact a high-pressure calcium silicate (CaSiO₃) was synthesised in a laboratory in 1975.

Of course, this is a challenge for minerals that only exist in a high-pressure phase. It requires special conditions, like being encased in diamond, for them to survive on reaching the Earth’s surface.

‘No one has ever successfully retrieved a high-pressure calcium silicate from the lower mantle before,’ commented Yingwei Fei, a geophysicist from the Carnegie Institution for Science in Washington DC who was not involved in the study.

This, he explained, ‘is because the high-pressure calcium silicate perovskite is “unquenchable”, meaning that it cannot retain its structure after being removed from its high-pressure environment.’

Back in 1975, scientists from the Australian National University did manage to synthesise this high-pressure phase in the laboratory by compressing calcium silicate in a so-called ‘diamond anvil cell’ that was heated to 1,400–1,800°C with a laser. 

The natural sample obtained by the researchers, Dr Fei noted, ‘shows an x-ray diffraction pattern consistent with that of the synthetic calcium silicate-perovskite high-pressure phase.’

The study was undertaken by mineralogist Oliver Tschauner of the University of Nevada, Las Vegas and his colleagues, who previously also discovered the only other natural sample of a high-pressure mineral, bridgmanite, in a shocked meteorite.

Calcium silicate perovskite, the team explained, is one of the most geochemically important minerals in the lower mantle, largely because it concentrates elements that are incompatible in the upper mantle.

These include rare-earth elements and long-lived radioactive isotopes like thorium and uranium that are important contributors to the heat of the mantle.

‘Our observations indicate that davemaoite also hosts potassium in addition to uranium and thorium in its structure,’ the researchers wrote in their paper.

‘Hence, the regional and global abundances of davemaoite influence the heat budget of the deep mantle, where the mineral is thermodynamically stable.’

Researchers led from the University of Nevada used synchrotron x-ray diffraction to characterise the crystalline compound, which they have called 'davemaoite'. Pictured: a reflected light, close-up image of the diamond in the X-ray beamline

Based on the team's results, davemaoite has now been confirmed as a new mineral by the International Mineralogical Association. Pictured: an x-ray diffraction map showing, in the centre, the davemaoite inclusion

The University of Nevada researchers used synchrotron-x-ray difffraction to identify the crystal compound they called “davemaoite”. The International Mineralogical Association has confirmed that davemaoite is a new mineral based on the results. Pictured is a reflected, close-up view of the diamond in the beamline (left), as well as an xray difffraction map that shows, in the middle, the davemaoite addition (right).

Tschauner and colleagues. In a similar Perspective, Yingwei Fei writes that it inspires hope for the discovery of more difficult high-pressure phase in nature. This can be done through careful searches in deep-origin meteorites or in deeply shocked diamonds. 

“Such direct sampling from the lower mantle, which is difficult to access, would help fill the knowledge gap regarding the chemical composition and heterogeneity in the whole mantle on our planet.” 

Science published the full results of this study. 

The diamond with the davemaoite inclusion was formed more than 410 miles (660 km) below the Earth's surface — and was unearthed in the Orapa mine in Botswana

The diamond with the davemaoite inclusion was formed more than 410 miles (660 km) below the Earth’s surface — and was unearthed in the Orapa mine in Botswana

HO-KWANG ‘DAVE’ MAO 

Professor Tschauner, along with colleagues confirmed that there was a natural-occurring high-pressure calcium silicate Perovskite sample. They decided to call it “davemaoite”.

It was done in honor of Ho-Kwang “Dave” Mao (80), a prominent Chinese-American geophysicist in deep-mantle petralogy. 

Dr Mao, who has conducted his research at the Geophysical Laboratory of the Carnegie Institution of Washington, is a prolific user of the diamond anvil cell, a tool which can create extremely high pressures in a laboratory setting.

His research highlights include the verification of a static pressure exceeding 1 Megabar and the identification of the structure and composition of the first high-temperature superconductor with a temperature critical to the boiling point liquid nitrogen.

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