Arakiite

Chemical formula: Zn₂+Mn₂+₁₂Fe₃+₂(As₃+O₃)(As₅+O₄)₂(OH)₂₃

Arakiite is an extremely rare zinc, manganese, and iron arsenite and arsenate, forming small, hexagonal, reddish-brown crystals.

## Characteristics Arakiite is a very rare mineral from the arsenite and arsenate group, chemically classified as a basic zinc, manganese, and iron arsenite and arsenate. It occurs as very small, tabular or platy crystals with a hexagonal outline, not exceeding 0.5 mm in diameter and 0.1 mm in thickness. These crystals often form rosetted or radiating aggregates. Its characteristic features include a deep, reddish-brown color and a vitreous luster. ## Physical Properties This mineral is characterized by a Mohs hardness of 3-4. It is brittle, and its crystals exhibit perfect cleavage in one direction, parallel to the crystal base. The luster is described as vitreous to slightly resinous. It is translucent to opaque in thicker fragments. ## Colors and Varieties Arakiite occurs in a uniform, deep reddish-brown color. No color varieties or commercial forms are known. ## History and Name The mineral was discovered in the Långban mine in Filipstad Municipality, Värmland County, Sweden. It was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 1998. Its name honors Takaharu Araki (1927-2016), a Japanese-American crystallographer from the University of Chicago, for his contributions to research on complex oxide structures and related minerals. ## Uses Due to its extreme rarity and microscopic crystal size, arakiite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals (so-called "micromounts").

Properties

Mohs hardness: 3-4
Luster: Vitreous to resinous
Streak: Light brown
Density: 4.53
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Trigonal

Diagnostic features

## Identification Amateur identification of arakiite is practically impossible. It requires advanced analytical methods, such as X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) to confirm its chemical composition. Preliminary identification in a collection relies on morphology (small, hexagonal, tabular crystals), characteristic reddish-brown color, vitreous luster, and, most importantly, knowledge of the locality (Långban) and associated minerals. ## Distinguishing from Similar Minerals Arakiite can be confused with other rare arsenates from Långban, such as hematolite, which forms similar aggregates but usually has more spherical aggregates and a slightly different hue. Distinguishing it from magnussonite or dixenite also requires laboratory analysis. The key distinguishing feature is the unique combination of chemical composition (presence of zinc, manganese, iron, and two forms of arsenic) and hexagonal crystal structure. ## Crystal Forms Arakiite crystallizes in the form of very small, thin, tabular crystals with a hexagonal outline. These crystals rarely occur individually, most often forming radiating or rosetted aggregates on the surface of the host rock.

Geological environment

## Genesis Arakiite is a mineral of metamorphic origin. It formed as a result of contact metamorphism of the iron and manganese ore deposit in Långban. It occurs in skarns, within dolomites and hausmannite-phlogopite rocks, filling small fractures and fissures. ## Mineral Associations This mineral occurs in association with other, often rare, minerals typical of the Långban deposit. It most commonly co-occurs with hausmannite, phlogopite, dolomite, barite, hematolite, magnussonite, dixenite, and unspecified minerals from the serpentine group. ## Localities The only confirmed locality for arakiite in the world is its type locality – the historic Långban mine, located in Filipstad Municipality, Värmland County, Sweden. This is one of the most famous mineralogical sites in the world, renowned for the occurrence of hundreds of unique and rare minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an arakiite specimen is primarily assessed based on the abundance and development of its crystals. Specimens with numerous, sharply defined, hexagonal crystals forming aesthetic, rosetted aggregates are most highly valued. Contrast with the rock matrix and the presence of interesting associated minerals are also important. Due to its microscopic size, clarity and transparency are not key criteria, although well-formed, translucent crystals are highly desirable. ## Popular Localities The only source of arakiite specimens is the Långban mine in Sweden. Specimens from this historic locality are highly prized by collectors specializing in rare minerals and "micromount" specimens.

Care and storage

## Cleaning Arakiite specimens, typically microscopic crystals on a rock matrix, are extremely delicate. Cleaning should be kept to an absolute minimum. If necessary, compressed air (from a safe distance) can be used to remove loose dust particles. Any contact with water or other chemicals should be avoided. ## What to Avoid Contact with water, acids, bases, and all solvents must be strictly avoided. The crystals are very brittle and soft, so any mechanical cleaning, including ultrasonics, which would instantly destroy the specimen, should be avoided. It should also be protected from high temperatures and sudden temperature changes. ## Storage Arakiite specimens should be stored exclusively in specialized micromount boxes, which protect them from dust, moisture, and mechanical damage. Exposure to direct sunlight should be avoided, although there is no evidence of fading.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FArakiite