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 und Impaktforschung
Nördlingen, Germany and colleagues at the German Research Centre for
Geoscience GFZ in Potsdam, Museum für Naturkunde Berlin, Natural History
Museum Vienna, Institute of Physics of the Czech Academy of Science, Natural
History Museum Oslo, University of Manchester, and Deutsches Zentrum für
Luft und Raumfahrt Berlin published their findings in the scientific journal
“American Mineralogist”.
Besides the about 382 kilograms of rocks and soils collected by the Apollo
and Luna missions, lunar meteorites allow valuable insights into the
formation of the Moon. They are ejected by impacts onto the lunar surface
and subsequently delivered to Earth.
Some of these meteorites experienced particularly high temperatures and
pressures. The extreme physical conditions often led to shock melting of
microscopic areas within these meteorites. These shocked areas are of great
relevance as they mirror pressure and temperature regimes similar to 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,
and bridgmanite, constitute large parts of the Earth’s mantle. Theses
crystals were synthesized in high-pressure laboratory experiments. As
natural minerals they were first described and named based on their
occurrences in meteorites.
The new mineral donwilhelmsite is the first high-pressure mineral found in
meteorites with application for subducted terrestrial sediments. It is
mainly composed of calcium, aluminum, silicon, and oxygen atoms.
Donwilhelmsite was discovered within shock melt zones of the lunar meteorite
Oued Awlitis 001 found in 2014 in the Western Sahara. This meteorite is
compositionally similar to rocks comprising the Earth’s continents. Eroded
sediments from these continents are transported by wind and rivers to the
oceans, and subducted into the Earth’s mantle as part of the dense oceanic
crust. While being dragged deeper into the Earth mantle the pressure and
temperature increases, and the minerals transform into denser mineral
phases. The newly discovered mineral donwilhelmsite forms in 460 to 700
kilometre depth. In the terrestrial rock cycle, donwilhelmsite is therefore
an important agent for transporting crustal sediments through the transition
zone separating the upper and lower Earth’s mantle.
This pan-European collaboration was essential to obtain the lunar meteorite,
recognize the new mineral, understand its scientific relevance, and to
determine the crystal structure of the tiny, the thousands part of a
millimeter thick, mineral crystal with high accuracy. "At the GFZ, we used
transmission electron microscopy to investigate microstructural aspects of
the samples," says Richard Wirth from the section "Interface Geochemistry".
"Our investigations and the crystal structure analyses of the colleagues
from the Czech Republic once again underline the importance of transmission
electron 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 and data analyses
of the Apollo space missions that brought to Earth the first rock samples
from the Moon. Part of the meteorite Oued Awlitis 001, acquired by
crowdfunding initiative „Help us to get the Moon!”, is on display at the
Natural History Museum Vienna.
Original study:
Fritz, J., Greshake, A., Klementova, M., Wirth, R., Palatinus L. L. ,
Trønnes, R. G., Assis Fernandes, V., Böttger, U., Ferrière, L, 2020.
American Mineralogist. Donwilhelmsite, [CaAl4Si2O11], a new lunar
high-pressure Ca-Al-silicate with relevance for subducted terrestrial
sediments. DOI:
10.2138/am-2020-7393
Tags:
Space & Astrophysics