Donwilhelmsite

Chemical formula: CaAl₄Si₂O₁₁

Donwilhelmsite is a rare calcium aluminum silicate, discovered in the Oued Awlitis 001 lunar meteorite, characterized by high density and hardness.

## Characteristics Donwilhelmsite is a mineral from the silicate group that forms microscopic inclusions in meteorite rocks. It typically occurs as very small, anhedral (not exhibiting its own crystallographic forms) grains not exceeding several tens of micrometers in size. Due to its size, its visual characteristics are difficult to assess without advanced analytical equipment, such as an electron microscope. ## Physical Properties This mineral is characterized by high hardness, estimated at 7 on the Mohs scale, and a significant density of approximately 3.63 g/cm³. It has a vitreous luster and is transparent. The calculated refractive index is 1.71. ## Colors and Varieties The observed grains of donwilhelmsite are colorless. No colored varieties or commercial forms are known. ## History and Name Donwilhelmsite was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2020 (IMA2019-111). Its name honors Don E. Wilhelms, an American planetary geologist who made significant contributions to the study of lunar geology and the mapping of its surface as part of the Apollo program. The mineral was discovered and described by an international team of scientists, including Jörg Fritz, Christian Schroeder, and Ansgar Greshake. ## Applications Donwilhelmsite has no industrial applications due to its extreme rarity and microscopic size. Its significance is purely scientific, as it provides information about high-pressure processes occurring in the Earth's crust and mantle, as well as on other celestial bodies.

Properties

Mohs hardness: 7
Luster: Vitreous
Streak: White
Density: 3.63
Cleavage: None
Fracture: Uneven
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of donwilhelmsite is possible only using advanced analytical techniques. This requires preparing a thin section from the meteorite specimen and performing chemical and structural analysis with an electron microscope (EDS/WDS analysis) and by electron backscatter diffraction (EBSD). Its high density and chemical composition are key diagnostic features. ## Distinguishing from Similar Minerals Based on appearance alone, it is impossible to distinguish it from other colorless, microscopic minerals co-occurring in meteorites, such as anorthite or olivine. It differs from them in chemical composition and crystal structure, which can only be determined by laboratory methods. ## Crystal Forms Donwilhelmsite occurs as anhedral (xenomorphic) grains, meaning it does not form its own well-developed crystal faces. It is observed as irregular inclusions within other minerals.

Geological environment

## Genesis Donwilhelmsite forms under very high pressure and temperature conditions. Its presence in the Oued Awlitis 001 lunar meteorite is a result of shock metamorphic processes that occurred during the impact of another celestial body on the Moon's surface. The pressure required for its formation is estimated to be between 4.5 and 6 GPa. It is believed that minerals with a similar structure may be a significant component of transition zones in the Earth's mantle. ## Mineral Associations This mineral co-occurs with other shock minerals and components of the meteorite in which it was found. In the type locality (Oued Awlitis 001 meteorite), its association with ringwoodite, wadsleyite, tissintite, anorthite, olivine, pigeonite, and ilmenite has been observed. ## Localities The only confirmed locality of donwilhelmsite is the Oued Awlitis 001 lunar meteorite, found in 2014 in the Western Sahara. It is a brecciated anorthosite that was ejected from the Moon's surface by an impact.

Rarity

Extremely rare

For collectors

## Quality Criteria Donwilhelmsite is not a mineral available on the collector's market in the form of isolated specimens. Its value is purely scientific. The only form in which it can be "possessed" is a fragment of the parent meteorite in which it was identified. In such a case, the value is determined by the meteorite itself (its type, size, history), and not by the presence of microscopic donwilhelmsite grains, which cannot be seen with the naked eye. ## Popular Localities The only known "locality" is the Oued Awlitis 001 meteorite.

Care and storage

## Cleaning Due to its occurrence as microscopic inclusions in meteorites, individual grains of donwilhelmsite are not subject to cleaning. Meteorite specimens containing this mineral should only be cleaned according to recommendations for the specific meteorite type, most often by dry methods, e.g., using a soft brush. ## What to Avoid Contact of the parent specimen with water, chemicals, as well as extreme changes in temperature and humidity, which could damage the entire meteorite, should be avoided. ## Storage Meteorite specimens containing donwilhelmsite should be stored under stable conditions, preferably in sealed containers with a desiccant (e.g., silica gel), away from direct sunlight and heat sources.

Sources

IMA Mineral List (CNMNC)