Donwilhelmsite is vital for understanding the inner structure of the planet Earth
A team of European researchers discovered a new high pressure mineral in the lunar meteorite Oued Awlitis 001 named donwilhelmsite [CaAl4Si2O11]. The team around Jörg Fritz from the Zentrum für Rieskrater & Impaktforschung Nördlingen, Germany & colleagues at the German Research Centre for Geoscience GFZ in Potsdam, Museum für Naturkunde Berlin, explanation Museum Vienna, Institute of Physics of the Czech Academy of Science, explanation Museum Oslo, University of Manchester & Deutsches Zentrum für Luft & Raumfahrt Berlin published their findings in the scientific journal American Mineralogist.
Besides the about 382 Kg of rocks & soils collected by the Apollo & Luna missions, lunar meteorites allow valuable insights into the formation of the Moon. They’re ejected by impacts onto the lunar surface & subsequently delivered to Earth.
Some of these meteorites experienced particularly high temperatures & pressures. The physical conditions often led to shock melting of microscopic areas in these meteorites. These shocked areas are of great relevance as they mirror pressure & temperature regimes almost like those prevailing in the Earth’s mantle. Therefore, the microscopic shock melt areas are natural crucibles hosting minerals that are otherwise naturally inaccessible at the Earth’s surface.
Minerals like wadsleyite, ringwoodite & bridgmanite, constitute large parts of the Earth’s mantle. These crystals were synthesized in high pressure laboratory experiments. As natural minerals, they were first described & named supported their occurrences in meteorites.
The new mineral donwilhelmsite is the first high pressure mineral found in meteorites with application for subducted terrestrial sediments. It’s mainly composed of calcium, aluminium, silicon & oxygen atoms. Donwilhelmsite was discovered in shock melt zones of the lunar meteorite Oued Awlitis 001 found in 2014 in the Western Sahara .
This meteorite is compositionally almost like rocks comprising the Earth’s continents. Eroded sediments from these continents are transported by wind & rivers to the oceans and subducted into the Earth’s mantle as a part of the dense oceanic crust. While being dragged deeper into the earth mantle the pressure & temperature increases and the minerals transform into denser mineral phases.
The newly discovered mineral donwilhelmsite forms in 460-700 kilometer depth. In the terrestrial rock cycle, donwilhelmsite is therefore a crucial agent for transporting crustal sediments through the transition zone separating the upper & lower Earth’s mantle.
This pan European collaboration was essential to get the lunar meteorite, recognize the new mineral, understand its scientific relevance & to work out the crystal structure of the small, the thousands a part of a millimeter thick, mineral crystal with high accuracy. “At the GFZ, we used transmission microscopy to research microstructural aspects of the samples” says Richard Wirth from the section “Interface Geochemistry”. “Our investigations & the crystal structure analyses of the colleagues from the Czech Republic once more underline the importance of transmission microscopy in the geosciences.”
The new mineral was named-in honor of the lunar geologist Don E. Wilhelms, an American scientist involved in landing site selection & data analyses of the Apollo space missions that delivered to Earth the primary rock samples from the Moon. A part of the meteorite Oued Awlitis 001 acquired by crowdfunding initiative “Help us to urge the Moon!”, is on display at the explanation Museum Vienna.