Akhtenskite
Chemical formula: Mn<sup>4+</sup>O<sub>2</sub>
A discredited mineral species, a hexagonal polymorph of manganese(IV) oxide, typically occurring as black, earthy aggregates.
Description
## Characteristics Akhtenskite is a historical name for a hexagonal polymorph of manganese(IV) oxide. In 2012, the mineral was discredited by the International Mineralogical Association (IMA) and is now considered a structural variant of ramsdellite or identical to it. It is no longer recognized as a distinct mineral species. It occurs as very fine-grained, earthy or sooty masses and coatings. Its appearance is inconspicuous, forming aggregates without well-formed crystals. ## Physical Properties It is usually soft and brittle, easily soiling fingers upon touch. The luster can be metallic on fresh surfaces, but is most often dull or earthy. It is completely opaque. Measured density ranges from 3.8 to 4.4 g/cm³, which is lower than the theoretical density due to the porous structure of the aggregates. ## Colors and Varieties Its color is uniform, from steel-gray to black. It does not form colored or commercial varieties. ## History and Name The name comes from the discovery locality – the Akhtenskoye (Ахтенское) manganese deposit in the Southern Urals, Russia. The mineral was described in 1980, but later, more precise structural studies showed its identity with other, previously described manganese oxides, which led to its disqualification as a separate mineral. ## Uses As a discredited mineral species, akhtenskite has no practical application. Specimens are of historical and scientific significance only, especially those from the type locality.
Diagnostic features
## Identification Identification of akhtenskite is impossible without advanced laboratory analyses, such as X-ray diffraction (XRD). In collector's conditions, it is simply "black manganese oxide." It forms soft, black, smudging aggregates with an earthy or dull surface. ## Distinguishing from Similar Minerals It is visually indistinguishable from other manganese oxides with which it often co-occurs, such as pyrolusite, cryptomelane, todorokite, or birnessite. All these minerals form similar black, earthy or reniform aggregates, often collectively referred to as "wad" or "psilomelane." ## Crystal Forms It does not form crystals visible to the naked eye. It occurs exclusively in the form of compact, earthy, sooty, or crusty aggregates, sometimes with a reniform or botryoidal structure.
Geological environment
## Genesis It is a secondary mineral, formed in the oxidation (weathering) zones of manganese ore deposits. It forms as a result of the alteration of primary manganese minerals, such as rhodochrosite or hausmannite, under low temperatures and pressures, with abundant oxygen access. ## Mineral Associations It most often occurs in association with other manganese and iron oxides and hydroxides, such as pyrolusite, ramsdellite, birnessite, cryptomelane, goethite, and hematite. ## Localities The type locality, from which historical specimens originate, is the Akhtenskoye deposit in the Southern Urals, Russia. As a structural phase, material corresponding to akhtenskite is likely a component of many manganese deposits worldwide, but is not identified under this name.
Rarity
Very rare
Collector aspects
## Quality Criteria Due to the mineral's status, the only criterion of value is its origin from the type locality (Akhtenskoye, Russia) and a historical label. The appearance of the specimen itself is of secondary importance, as these are usually shapeless, black masses. The richer the aggregate on the rock matrix, the more interesting the specimen. ## Popular Localities For collectors seeking historical "akhtenskite" specimens, the only significant location is the type locality in the Urals, Russia.
Care and storage
## Cleaning Akhtenskite specimens should not be wet cleaned. They are very brittle and soft. To remove dust, a very soft, dry brush can be used, or dust can be carefully blown off with compressed air from a distance. ## What to Avoid Avoid contact with water and any chemicals that may react with manganese oxides. Ultrasonic cleaners are absolutely forbidden. The mineral is soft, so it must be protected from scratching and abrasion. ## Storage It is recommended to store specimens in closed, padded boxes to prevent crumbling and dusting. Protect from shocks and falls.