Researchers have discovered a new mineral in a meteorite from the Moon. Named donwilhemsite, the mineral appears to form under high pressures and may play a crucial role in the rock cycle deep within the Earth.

Made mostly of calcium, aluminum, silicon and oxygen atoms, donwilhelmsite was discovered in a meteorite called Oued Awlitis 001, which was found in 2014 in the Western Sahara desert. The team used transmission electron microscopes to study a sample of the meteorite and identify the crystal structure of the new mineral.

Specifically, donwilhelmsite was found in the meteorite’s shock melt zones, where the rock melts in the immense pressure and temperature as it hurtles into the Earth’s atmosphere and collides with the surface, then later cools and hardens again.

Interestingly, these conditions are similar to those found deep within our planet’s mantle, giving us a handy glimpse into the kinds of minerals that might be down there, where we can’t easily study them. With that in mind, the researchers say that donwilhelmsite could be naturally forming at depths between 460 and 700 km (285 and 435 miles) below the surface.

Since this meteorite is composed of rocks similar to those that make up the Earth’s crust, the team believes that donwilhelmsite probably plays a key role in transporting sediments from the crust – in the form of ancient tectonic plates being pushed deep into the planet – down through the transition zone, which separates the upper and lower mantle.

If donwilhelmsite sounds like a name, well that’s because it is. The new mineral was named after Don Wilhelms, a lunar geologist who was part of the team that analyzed data and samples returned from the Apollo missions.

https://newatlas.com/science/donwilhelmsite-new-mineral-moon-meteorite/

Interesting but it would be good to have more details

dv said:

Interesting but it would be good to have more details

Original article behind a “members only” wall.

The empirical formula calculated on the basis of 7 cations is Ca1.02 Al3.92 Si2.06 O11, and the simplified formula is Ca Al4 Si2 O11.

From http://www.minsocam.org/msa/ammin/toc/2020/Abstracts/AM105P1704.pdf

We report on the occurrence of a new high-pressure Ca-Al-silicate in localized shock melt pockets found in the feldspatic lunar meteorite Oued Awlitis 001. The new mineral crystallized as tiny, micrometer-sized, acicular grains in shock melt pockets of roughly anorthitic bulk composition. The new mineral has a hexagonal structure. Needles crystallized in ~0.2 mm sized shock melt pockets of anorthositic-like chemical composition.

Transmission electron microscopy reveals that the Ca Al4 Si2 O11 crystals are identical to the calcium aluminum silicate (CAS) phase first reported from static pressure experiments.

The International Mineralogical Association (IMA) has approved this naturally formed CAS phase as the new mineral “donwilhelmsite” , honoring the U.S. lunar geologist Don E. Wilhelms. On the Moon, donwilhelmsite can form from the primordial feldspathic crust during impact cratering events

Shock melt pockets in meteorites serve as natural crucibles mimicking the conditions expected in the Earth’s mantle. Donwilhelmsite forms in the Earth’s mantle during deep recycling of aluminous crustal materials, and is a key host for Al and Ca of subducted sediments in most of the transition zone and the uppermost lower mantle (460–700 km). Donwilhelmsite bridges the gap between kyanite at low pressures and the Ca-perovskite at high-pressures. In ascending buoyant mantle plumes, at about 460 km depth, donwilhelmsite is expected to break down into minerals such as garnet, kyanite, and clinopyroxene.

dv said:

Interesting but it would be good to have more details

Abstract
We report on the occurrence of a new high-pressure Ca-Al-silicate in localized shock melt pockets found in the feldspatic lunar meteorite Oued Awlitis 001 and discuss the implications of our discovery. The new mineral crystallized as tiny, micrometer-sized, acicular grains in shock melt pockets of roughly anorthitic bulk composition. Transmission electron microscopy based three-dimensional electron diffraction (3D ED) reveals that the CaAl4Si2O11 crystals are identical to the calcium aluminum silicate (CAS) phase first reported from static pressure experiments. The new mineral has a hexagonal structure, with a space group of P63/mmc and lattice parameters of a = 5.42(1) Å; c = 12.70(3) Å; V = 323(4) Å3; Z = 2. This is the first time 3D ED was applied to structure determination of an extraterrestrial mineral. The International Mineralogical Association (IMA) has approved this naturally formed CAS phase as the new mineral “donwilhelmsite” , honoring the U.S. lunar geologist Don E. Wilhelms. On the Moon, donwilhelmsite can form from the primordial feldspathic crust during impact cratering events. In the feldspatic lunar meteorite Oued Awlitis 001, needles of donwilhelmsite crystallized in ~200 mm sized shock melt pockets of anorthositic-like chemical composition. These melt pockets quenched within milliseconds during declining shock pressures. Shock melt pockets in meteorites serve as natural crucibles mimicking the conditions expected in the Earth’s mantle. Donwilhelmsite forms in the Earth’s mantle during deep recycling of aluminous crustal materials, and is a key host for Al and Ca of subducted sediments in most of the transition zone and the uppermost lower mantle (460–700 km). Donwilhelmsite bridges the gap between kyanite and the Ca-component of clinopyroxene at low pressures and the Al-rich Ca-ferrite phase and Ca-perovskite at high-pressures. In ascending buoyant mantle plumes, at about 460 km depth, donwilhelmsite is expected to break down into minerals such as garnet, kyanite, and clinopyroxene. This process may trigger minor partial melting, releasing a range of incompatible minor and trace elements and contributing to the enriched mantle (EM1 and EM2) components associated with subducted sedimentary lithologies.

https://pubs.geoscienceworld.org/msa/ammin/article-abstract/105/11/1704/592180/Donwilhelmsite-CaAl4Si2O11-a-new-lunar-high?redirectedFrom=fulltext

> https://pubs.geoscienceworld.org/msa/ammin/article-abstract/105/11/1704/592180/Donwilhelmsite-CaAl4Si2O11-a-new-lunar-high?redirectedFrom=fulltext

Thanks! You broke the “members only” restriction. This opens the full paper on Sci-Hub.

The Earth’s continental crust and the lunar highlands (i.e., consisting of materials derived from many superposed impact ejecta from all crustal levels and covering the lunar surface) are dominantly felsic in composition, including as major elements, O, Si, Al, Ca, Na, and K. Minerals controlling the distribution of these elements are important agents for the origin and fate of planetary crusts. Remnants of a primordial crust are preserved on the Moon.

Fifty years ago, the Apollo 11 mission collected 21.6 kg of lunar rocks and soils, including anorthosites. From these samples, it was concluded that the impact gardened bright lunar highlands derived from a primordial (>4.3 Ga old) anorthositic crust, several tens of kilometers thick.

On Earth, during plate tectonic processes, crustal materials rich in volatiles and other elements incompatible in mantle minerals are reintroduced into the depleted mantle by subduction. About 75% of the subducted sediment flux is estimated to be direct terrigenous material of average upper crust composition. Deep recycling of continentally derived sediments below 200–300 km depth is facilitated by stepwise densification at 6.5 GPa (~200 km depth), when orthoclase breaks down, and at 9 GPa (~300 km depth) when hollandite and stishovite form. At deeper levels, the sediment and peridotite densities may remain nearly identical to depths beyond 1200 km and ~40 GPa.

Localized zones of shock melt in moderately to strongly shocked mete-orites present a natural environment in which a hot and compressed melt is quenched at typical deep mantle pressures to temperatures low enough to inhibit a back reaction into low-pressure mineral assemblages during pressure release.