Allabogdanite
Chemical formula: (Fe,Ni)<sub>2</sub>P
An extremely rare iron-nickel phosphide, known primarily from the Onello iron meteorite, forming microscopic, metallic grains.
Description
## Characteristics Allabogdanite is a mineral from the phosphide group, chemically classified as an iron-nickel phosphide. It occurs as very small, platy or granular aggregates, usually of microscopic size. It is an opaque mineral with a metallic luster. In reflected light under a microscope, its color is described as grayish with a pinkish or yellowish tint. Due to its composition and origin, it is primarily of interest in scientific research in mineralogy and meteoritics. ## Physical Properties Allabogdanite has a hardness ranging from 5-6 on the Mohs scale. Its luster is distinctly metallic. It is a brittle and opaque mineral. The density calculated based on its chemical composition and unit cell parameters is approximately 7.13 g/cm³. ## Colors and Varieties This mineral does not exhibit color variation. Its appearance is constant, and the observed slight differences in shades result from observation conditions in reflected light. No varieties are known. ## History and Name Allabogdanite was officially recognized by the International Mineralogical Association (IMA) in 1997. Its name honors the Russian geologist Dr. Alla V. Bogdanova of the All-Russian Geological Research Institute (VSEGEI) in St. Petersburg. It was discovered and described based on material from the Onello iron meteorite, found in the Onello River basin on the Aldan Plateau in Yakutia (Russia). ## Uses Allabogdanite has no commercial or industrial applications. Its significance is purely scientific, as an indicator of specific formation conditions of meteorite parent bodies. It is also sought after by specialized collectors of rare minerals and meteorites.
Diagnostic features
## Identification Identification of allabogdanite is impossible without advanced analytical techniques. Due to its microscopic size and occurrence as inclusions, it cannot be recognized based on visual characteristics. Definitive identification requires the use of a metallographic microscope for observation in reflected light and chemical analysis using an electron microprobe (EDS/WDS) to confirm the presence of iron, nickel, and phosphorus in appropriate proportions. Final confirmation is achieved through crystal structure analysis by X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Allabogdanite can be confused with other iron-nickel phosphides found in meteorites, primarily schreibersite ((Fe,Ni)₃P) and nickelphosphide ((Ni,Fe)₃P). Differentiation is based solely on chemical analysis, which shows a different ratio of metal atoms to phosphorus (2:1 for allabogdanite, 3:1 for schreibersite and nickelphosphide), and on crystal structure examination. ## Crystal Forms Allabogdanite forms fine, platy (lamellar) or irregular, granular aggregates. It often occurs as plates formed by exsolution processes within larger crystals of other minerals, such as taenite.
Geological environment
## Genesis Allabogdanite is a mineral that forms under extremely reducing conditions, with very low oxygen fugacity. Such an environment is characteristic of the interiors of planetesimals, from which iron meteorites originate. It forms during the very slow cooling of an iron-nickel melt, resulting in the crystallization or exsolution of phosphide phases. Beyond meteorites, its occurrence has been noted in rocks of the Hatrurim Formation in Israel, where it formed as a result of natural pyrometamorphism. ## Mineral Associations In the Onello meteorite, allabogdanite coexists with kamacite, taenite, plessite, schreibersite, and nickelphosphide. In the terrestrial locality in Israel, it is accompanied by native iron, pyrite, and other high-temperature minerals. ## Localities The most important and type locality is the Onello iron meteorite, found in Yakutia, Russia. This mineral has also been identified in the Hishikari gold mine in Japan and in pyrometamorphic rocks of the Hatrurim Formation in the Dead Sea region of Israel and Palestine.
Rarity
Extremely rare
Collector aspects
## Quality Criteria The quality of an allabogdanite specimen is assessed differently than for typical minerals. Since it occurs as microscopic inclusions, the most important criterion is the certainty of scientifically confirmed identification. A specimen is usually a polished slice of a meteorite. Its value depends on the size and quality of the meteorite itself, and the presence of documented allabogdanite is a valuable addition for specialized collectors. The size and abundance of allabogdanite grains, visible under a microscope, also increase its scientific and collectible value. ## Popular Localities The only source of specimens that may enter the collector's market is the Onello meteorite. Other localities are of purely scientific importance and do not provide material for collections.
Care and storage
## Cleaning Specimens containing allabogdanite, which are typically meteorite fragments, should not be cleaned. The mineral occurs as microscopic inclusions, and any attempt at mechanical or chemical cleaning can destroy not only the allabogdanite itself but also the surrounding valuable meteoritic material. ## What to Avoid Contact with water, moisture, and all chemicals, especially acids, which can react with phosphides, should be strictly avoided. High temperatures and thermal shock should also be avoided. As a meteoritic mineral, it is sensitive to terrestrial conditions, especially oxidation. ## Storage It is recommended to store specimens under stable, dry conditions. The best solution is to place the specimen in a sealed container, such as a membrane box or a display case with a desiccant, to minimize the risk of oxidation and degradation.