Rusakovite

Chemical formula: (Fe₃+,Al)₅(V₅+O₄)₂(OH)₉·₃H₂O

Rusakovite is a rare iron and aluminum vanadate, forming small, spherical aggregates with a characteristic yellowish-brown color.

## Characteristics Rusakovite is a hydrated iron and aluminum vanadate, occurring extremely rarely. It forms characteristic spherical or globular aggregates with a radial internal structure, reaching up to 2 mm in diameter. It also occurs as earthy or powdery coatings and masses. Due to the nature of the aggregates, individual crystals are not observed. ## Physical Properties This mineral is very soft and brittle. Its luster is described as dull or earthy, and on fresh fractures, it can be slightly waxy. It is opaque. The calculated density is approximately 3.45 g/cm³. ## Colors and Varieties Rusakovite typically ranges in color from yellowish-brown to reddish-brown. Some sources mention shades from light yellow to almost orange. No varieties are distinguished. ## History and Name The mineral was first described in 1960 by E.A. Ankinovich. The name honors Mikhail Petrovich Rusakov (1892-1963), a Soviet geologist and specialist in ore deposits, who was a member of the Kazakh Academy of Sciences. ## Uses Rusakovite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and for scientists.

Properties

Mohs hardness: 1
Luster: Dull
Streak: Yellow-brown
Density: 3.45
Cleavage: None
Fracture: Earthy
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Key diagnostic features include its occurrence as small, radial spheres, characteristic yellowish-brown color, dull luster, and extreme softness. Its association with other vanadates in sedimentary rocks is also an important indicator. ## Differentiation from Similar Minerals Rusakovite can be confused with other secondary vanadium minerals, such as carnotite or tyuyamunite, which, however, usually have a brighter, yellow color and often exhibit fluorescence under UV light, which rusakovite does not. It can also be mistaken for other earthy iron oxides (e.g., goethite), but chemical tests will reveal the presence of vanadium. ## Crystal Forms This mineral does not form well-developed crystals. It occurs exclusively as spherulitic (globular) aggregates with a radial internal structure and as earthy coatings and masses.

Geological environment

## Genesis Rusakovite is a secondary mineral, forming in the oxidation zones of vanadium deposits. Its formation is associated with the weathering of primary vanadium-bearing minerals under strongly oxidizing conditions, in the presence of iron and aluminum. It is most commonly found in sedimentary carbonate-siliceous rocks. ## Mineral Associations This mineral co-occurs with other vanadium minerals, such as hewettite, pascoite, satpaevite, as well as gypsum, calcite, and clay minerals. ## Localities The most important and typical occurrence of rusakovite is the Kurumsak vanadium deposit in the Karatau Range in southern Kazakhstan. This is the only confirmed and well-documented locality for this mineral worldwide.

Rarity

Extremely rare

For collectors

## Quality Criteria The most desirable specimens for collectors are those with well-formed, distinct spherules (globules) of an intense, yellowish-brown color, contrasting with the rock matrix. The size of the aggregates and their abundance on the specimen's surface significantly increase its value. Due to its rarity, even small but distinct masses are prized. ## Popular Localities The only source of collector specimens is the historical type locality – the Kurumsak deposit in Kazakhstan.

Care and storage

## Cleaning Due to its extreme brittleness and softness, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used from a distance to blow off loose dust. Contact with water should be avoided, as it can affect the mineral's hydrated structure. ## What to Avoid All chemicals, especially acids, which will easily dissolve it, should be avoided. The mineral is very soft, so it must be protected from any touch, abrasion, or vibrations. Changes in humidity and temperature should be avoided. ## Storage Rusakovite specimens should be stored in stable conditions, in closed "micromount" boxes, to protect them from mechanical damage and dust. They should not be exposed to direct sunlight or moisture.

Sources

IMA Mineral List (CNMNC)