Antitaenite

Chemical formula: (Ni,Fe)

Antitaenite is a rare, metallic nickel-iron mineral, found almost exclusively in meteorites.

## Characteristics Antitaenite is a metallic mineral from the native elements group, composed mainly of nickel and iron. It is a polymorph of taenite, meaning it has the same chemical composition but a different crystal structure. It occurs as microscopic grains and lamellae in iron meteorites, especially in nickel-rich ataxites. Its identification requires advanced analytical methods, such as X-ray diffraction, due to its occurrence as fine intergrowths with other Fe-Ni phases, such as taenite and kamacite. ## Physical Properties As a metal, antitaenite is opaque and has a metallic luster. Its hardness and density are similar to other iron-nickel alloys, but precise values are difficult to measure due to the microscopic size of the grains. ## History and Name The name "antitaenite" refers to its relationship with taenite and its different (anti-) crystallographic structure. It was described as a new mineral phase in the 1990s after detailed studies of nickel-rich meteorites, such as the Estherville meteorite.

Properties

Mohs hardness
5-6
Luster
Metallic
Streak
Gray
Density
8.0-8.2
Cleavage
None
Fracture
Hackly
Transparency
Opaque
Crystal system
Cubic

Diagnostic features

## Identification Antitaenite is impossible to identify visually or by standard gemological tests. Its confirmation requires specialized laboratory techniques, such as metallography, electron microprobe (EDS/WDS), and X-ray diffraction (XRD), which allow for the analysis of crystal structure and chemical composition at the micro-scale. ## Distinguishing from Similar Minerals Under the microscope, it is distinguished from co-occurring minerals – kamacite (less nickel) and taenite (different crystal structure) – based on chemical composition and crystallographic properties. Visually, they are indistinguishable. ## Crystal Forms Antitaenite forms microscopic, platy or irregular grains within the larger metallic mass of the meteorite.

Geological environment

## Genesis Antitaenite forms as a result of extremely slow cooling (on the order of a few degrees Celsius per million years) of the iron-nickel alloy in the cores of planetesimals, from which meteorites originate. It forms within a specific range of temperatures and chemical composition (high nickel content, above 30%). ## Mineral Associations This mineral occurs in close association with other meteoritic minerals, mainly taenite, kamacite, and tetrataenite. It may also co-occur with troilite and schreibersite. ## Localities Antitaenite has been identified in nickel-rich iron meteorites (ataxites) and in metallic fragments of some mesosiderites. Confirmed occurrences include meteorites such as Estherville (USA), San Cristobal (Chile), and Tlacotepec (Mexico).

Rarity

Very rare

For collectors

## Quality Criteria Antitaenite as such is not an object of collector trade due to its microscopic form. Collectible value is attributed to the entire meteorite in which it has been identified. For meteorite collectors, the type of meteorite (ataxites are rarer), its mass, history, and the quality of specimen preservation (lack of excessive corrosion) are important. Owning a specimen with confirmed presence of rare phases, such as antitaenite, can increase its scientific value and prestige in specialized collections.

Care and storage

## Cleaning Meteorite specimens containing antitaenite are stable, but should only be dry-cleaned, using a soft brush to remove dust. Water can accelerate the oxidation (rusting) of other iron minerals present in the meteorite. ## What to Avoid All moisture and chemicals are harmful. Prolonged exposure to humid air leads to corrosion. Acids should be avoided, as they could destroy delicate structures within the meteorite. ## Storage Meteorites with antitaenite are best stored in a dry environment, preferably in an airtight container with a desiccant (e.g., silica gel). Stable room temperature is suitable.

External references

Sources

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