Poirierite

Chemical formula: Mg₂SiO₄

Poirierite is a high-pressure polymorph of forsterite, occurring naturally in meteorites and as inclusions in diamonds.

## Characteristics Poirierite is a silicate mineral, a high-pressure, tetragonal variety of forsterite (Mg₂SiO₄), also known as wadsleyite-II. It occurs as microscopic grains or inclusions, making its macroscopic features difficult to observe. It is colorless and has a vitreous luster. Its significance is primarily scientific, serving as an indicator of ultra-high pressure conditions prevailing in the Earth's mantle or during cosmic shock events. ## Physical Properties It is characterized by a hardness of approximately 7 on the Mohs scale and a density of 3.47 g/cm³. It is a transparent mineral with a white streak. ## History and Name The mineral's name honors Jean-Paul Poirier, a French physicist and geophysicist, for his contributions to the study of mantle minerals. The mineral was officially recognized by the International Mineralogical Association (IMA) in 2018. Its discovery in nature, in the Tenham meteorite, confirmed the existence of a mineral phase previously obtained only under laboratory conditions. ## Applications Poirierite has no commercial or industrial applications. Its value is purely scientific, providing data on processes occurring deep within the Earth's mantle and on the history of meteorite impacts.

Properties

Mohs hardness: 7
Luster: Vitreous
Streak: White
Density: 3.326
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of poirierite is possible only through advanced laboratory techniques, such as transmission electron microscopy (TEM) and electron diffraction. It is unrecognizable under collector and field conditions. ## Distinguishing from similar minerals It is distinguished from other Mg₂SiO₄ polymorphs (forsterite, wadsleyite, and ringwoodite) by its tetragonal crystal structure and specific physical properties observed at the atomic scale. Wadsleyite crystallizes in the orthorhombic system, and ringwoodite in the cubic system. ## Crystal forms Poirierite forms microscopic, tabular or bladed crystals, often less than one micrometer in size. They occur as aggregates in shock veins within meteorites.

Geological environment

## Genesis Poirierite forms under conditions of extremely high pressure (above 14 GPa) and high temperature. Its formation is associated with two main situations: shock metamorphism caused by meteorite impact into olivine-rich rocks, or crystallization under deep Earth mantle conditions, at depths of 400-525 km. ## Mineral associations In meteorites, poirierite co-occurs with other high-pressure minerals such as wadsleyite, ringwoodite, akimotoite, bridgmanite, and majorite. As inclusions in diamonds, it is accompanied by diamond and other deep mantle minerals. ## Localities Confirmed occurrences of poirierite are extremely rare. It has been identified in the Tenham meteorite (L6 chondrite), which fell in Queensland, Australia, and as inclusions in diamonds from the Orapa mine in Botswana.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of a poirierite specimen is identical to the quality of the host rock – a meteorite fragment or diamond. For meteorites, the size of the fragment, the presence of a fusion crust, and well-developed shock veins are important. Scientific value is the primary criterion, not aesthetics. ## Popular localities The only source of specimens available on the collector's market (though still extremely rare and primarily intended for institutions) is the Tenham meteorite from Australia.

Care and storage

## Cleaning Due to its microscopic nature and occurrence as inclusions, specimens containing poirierite (e.g., meteorite fragments) should be cleaned using methods appropriate for the main material, typically with compressed air or very delicate, dry brushes. ## What to avoid Avoid contact with chemicals, ultrasonics, and extreme temperature changes, which could damage both the mineral itself and the host rock. ## Storage Specimens should be stored in stable conditions, in a dry environment, away from direct sunlight and dust. Enclosed collector boxes or display cases are best suited.

External references

https://www.mindat.org/min-54351.html