Amakinite

Chemical formula: Fe<sup>2+</sup>(OH)<sub>2</sub>

Amakinite is a rare iron(II) hydroxide of the brucite group, characterized by its instability and rapid darkening in air.

## Characteristics Amakinite is a mineral belonging to the brucite group, being its iron analogue. It typically forms fine-grained, scaly or platy aggregates. Well-formed crystals are rarely observed. Its most characteristic feature is chemical instability – it rapidly oxidizes upon contact with atmospheric oxygen, leading to an irreversible change in color and chemical composition. Freshly exposed specimens are pale green or greenish-yellow, but over time they darken, turning into brown and black decomposition products, mainly goethite. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3.5-4. It exhibits excellent unidirectional cleavage, typical for minerals of the brucite group. On cleavage planes, a pearly luster is visible, while on other surfaces it can be vitreous. It is a translucent mineral. Its density is approximately 3.01 g/cm³. ## Colors and Varieties The typical color of fresh amakinite is pale green or yellowish-green. The oxidation process causes it to darken to brown, and eventually black, hues. There are no distinct color varieties or commercial forms – the color variability is a result of its decomposition, not primary crystallization. ## History and Name The mineral's name comes from the Amakinskaya Geological Expedition, which conducted research in Siberia, where the mineral was discovered. It was first described in 1962 in the Udachnaya kimberlite pipe in Eastern Siberia, in today's Sakha Republic (Yakutia), Russia. ## Uses Due to its rarity and instability, amakinite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized systematic collections.

Properties

Mohs hardness
3.5-4
Luster
Pearly
Streak
Pale green
Density
3.01
Cleavage
Perfect on {0001}
Transparency
Translucent
Crystal system
Trigonal

Diagnostic features

## Identification The key diagnostic feature of amakinite is its rapid color change from pale green to dark brown or black upon exposure to air. Other helpful features include low hardness, excellent cleavage, pearly luster on its surfaces, and occurrence in a specific geological environment (kimberlites). ## Distinguishing from Similar Minerals Amakinite can be confused with its magnesium analogue, brucite, which has very similar physical properties but is stable and does not darken in air. It may also resemble some minerals from the serpentine or chlorite groups, which are, however, harder than it and, most importantly, chemically stable. Final differentiation often requires chemical analysis confirming the dominance of iron. ## Crystal Forms Amakinite most often occurs as fine-grained, scaly, or platy aggregates. Well-formed, hexagonal tabular crystals are extremely rare and found in microscopic sizes.

Geological environment

## Genesis Amakinite forms under strongly reducing conditions, with low oxygen fugacity. It is a secondary mineral, formed by hydrothermal alteration of iron-rich minerals, mainly olivine. It is most commonly found in kimberlite pipes. ## Mineral Associations This mineral co-occurs with minerals typical of the kimberlite environment and reducing conditions. These include magnetite, cohenite, moissanite, native iron, as well as minerals from the serpentine and olivine groups. ## Localities The most important and classic locality for amakinite is the kimberlite pipes in the Sakha Republic (Yakutia), Russia, particularly the Udachnaya pipe. Its presence has also been noted in some meteorites, indicating its formation under extraterrestrial conditions.

Rarity

Very rare

For collectors

## Quality Criteria In the case of such a rare and unstable mineral, the main criterion for value is the mere fact of possessing a documented specimen. Samples that were secured immediately after extraction and show the least degree of oxidation, retaining their original, pale green color, are most highly prized. The size of amakinite aggregates and its association with other rare minerals are also important. ## Popular Localities The only source of collectible amakinite specimens is the Russian kimberlite deposits in Yakutia. Specimens from the type locality (Udachnaya pipe) are most sought after by specialized collectors of rare and systematic minerals.

Care and storage

## Cleaning Cleaning amakinite is highly inadvisable. Due to its extreme reactivity and softness, any attempt at wet or mechanical cleaning leads to its damage or destruction. If necessary, a gentle stream of compressed air can be used to remove loose dust particles. ## What to Avoid Contact of the mineral with air and moisture should be strictly avoided. Atmospheric oxygen causes its rapid and irreversible oxidation. All chemicals, especially acids, are also damaging to it. Specimens should not be heated or exposed to sunlight. ## Storage Amakinite requires specialized storage conditions. The best method is to place the specimen in an airtight container filled with an inert gas (e.g., argon). Alternatively, it can be stored in a container with a moisture and oxygen absorber. Some specimens are stored submerged in paraffin oil, which limits air access.

External references

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