Scientists discover new forms of feldspars

June 01, 2020

In high-pressure experiments, scientists have discovered new forms of the common mineral feldspar. At moderate temperatures, these hitherto unknown variants are stable at pressures of Earth's upper mantle, where common feldspar normally cannot exist. The discovery could change the view at cold subducting plates and the interpretation of seismologic signatures, as the team around DESY scientist Anna Pakhomova and Leonid Dubrovinsky from Bayerisches Geoinstitut in Bayreuth report in the journal Nature Communications.

Feldspars represent a group of rock forming minerals that are highly abundant on Earth and make up roughly 60 per cent of Earth's crust. The most common feldspars are anorthite, (CaSi2Al2O8), albite (NaAlSi3O8), and microcline (KAlSi3O8). At ambient conditions, the aluminium and silicon atoms in the crystal are each bonded to four oxygen atoms, forming AlO4 and SiO4 tetrahedra.

"The behaviour of feldspars under increasing pressure and temperature has been intensively investigated before, with the respect to their fate in Earth's interior," explains Pakhomova. "Feldspars are known to be stable only at pressures of up to 3 Giga-Pascals along the common pressure-temperature profile of the Earth, while they decompose into denser minerals at higher pressures." 3 Giga-Pascals (GPa) are equivalent to 30,000 times the normal air pressure at sea level. "However, under cold conditions feldspars may persist metastably at pressures higher than 3 GPa," adds Pakhomova. "Previous high-pressure structural studies of feldspars at room temperature have shown that the tetrahedral framework of feldspars is preserved up to 10 GPa."

The scientists now subjected common feldspars to pressures of up to 27 GPa and analysed their structure at the Extreme Conditions Beamline P02.2 of DESY's X-ray light source PETRA III and at the Advanced Photon Source (APS) in Chicago. "At pressures above 10 GPa, we have discovered new high-pressure polymorphs of anorthite, albite and microcline," reports Pakhomova. "The phase transitions are induced by severe geometrical distortions of AlO4 and SiO4 tetrahedra, which result in the aluminium and silicon atoms gaining additional neighbouring atoms and also in the formation of denser frameworks based on polyhedra where one aluminium or silicon atom is bonded to four, five or six oxygen atoms."

To investigate the stability of the discovered high-pressure variants of feldspars at high temperatures and their possible persistence in Earth's interior, the scientists performed a series of high-pressure-high-temperature experiments at the Bayerisches Geoinstitut. It turned out that the high-pressure variant of anorthite persists at temperatures up to 600 degrees Celsius at 15 GPa.

"Such pressure-temperature conditions could be found on Earth in the subductions zones - regions where two lithospheric plates collide, one riding over the other," explains Dubrovinsky. "In such geological settings, feldspars are delivered into Earth's interior along with other crustal material by the descending plate. Our results indicate that in cold subduction zones, if the temperature does not rise above 600 degrees, high-pressure phases derived from feldspars could persist at depths corresponding to Earth's upper mantle. This could possibly influence the dynamics and fate of cold subducting lithospheric plates and alter seismological signatures."
-end-
Scientists from Universität Bayreuth, Saint Petersburg State University, the University of Chicago, Bayerisches Geoinstitut and DESY contributed to this research.

DESY is one of the world's leading particle accelerator centres and investigates the structure and function of matter - from the interaction of tiny elementary particles and the behaviour of novel nanomaterials and vital biomolecules to the great mysteries of the universe. The particle accelerators and detectors that DESY develops and builds at its locations in Hamburg and Zeuthen are unique research tools. They generate the most intense X-ray radiation in the world, accelerate particles to record energies and open up new windows onto the universe. DESY is a member of the Helmholtz Association, Germany's largest scientific association, and receives its funding from the German Federal Ministry of Education and Research (BMBF) (90 per cent) and the German federal states of Hamburg and Brandenburg (10 per cent).

Reference: Polymorphism of feldspars above 10 GPa; Anna Pakhomova, Dariia Simonova, Iuliia Koemets, Egor Koemets, Georgios Aprilis, Maxim Bykov, Liudmila Gorelova, Timofey Fedotenko, Vitali Prakapenka, Leonid Dubrovinsky; Nature Communications, 2020; DOI: 10.1038/s41467-020-16547-4

Deutsches Elektronen-Synchrotron DESY

Related Temperatures Articles from Brightsurf:

CMIP6 adds more value in simulating extreme temperatures in China
CMIP6 adds more value in simulating extreme temperatures in China.

High temperatures threaten the survival of insects
Insects have difficulties handling the higher temperatures brought on by climate change, and might risk overheating.

Slinging ink, raising temperatures
You've heard that they can sag with age, perpetuate the name of a regrettable ex, or reveal an embarrassing inability to spell.

Warming temperatures are driving arctic greening
As Arctic summers warm, Earth's northern landscapes are changing. Using satellite images to track global tundra ecosystems over decades, a new study found the region has become greener, as warmer air and soil temperatures lead to increased plant growth.

A quantum thermometer to measure the coldest temperatures in the universe
The physicists' proposed thermometer is based on quantum entanglement and can accurately measure temperatures a billion times colder than those in outer space.

Warmer temperatures slow COVID-19 transmission, but not by much
Researchers at Mount Auburn Hospital looked at the impact of temperature, precipitation, and UV index on COVID-19 case rates in the United States during the spring months of 2020.

New 'refrigerator' super-cools molecules to nanokelvin temperatures
MIT physicists have found a way to cool molecules of sodium lithium down to 200 billionths of a Kelvin, just a hair above absolute zero.

An alloy that retains its memory at high temperatures
Even after the hundredth time the material returns to its original shape when heated.

New catalysts remove NOx pollutants at lower temperatures
Scientists from Tokyo Metropolitan University have developed a low-temperature catalyst for removing NOx gas from industrial exhaust using ammonia.

Cold temperatures linked to high status
Researchers have discovered that people associate cold temperatures with luxury items, which is important for companies that are trying to promote products that convey high status.

Read More: Temperatures News and Temperatures Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.