Potassic-ferri-leakeite

Chemical formula: KNa₂(Mg₂Fe₃+₂Li)Si₈O₂₂(OH)₂

Potassic-ferri-leakeite is a rare silicate from the amphibole group, distinguished by its complex chemical composition and dark color.

## Characteristics Potassic-ferri-leakeite is a complex chain silicate belonging to the amphibole supergroup. This mineral forms prismatic, elongated crystals, often occurring as fibrous aggregates or radial clusters. Its color is typically black or very dark green, which is characteristic of iron-rich amphiboles. It is opaque and has a vitreous luster. ## Physical Properties Potassic-ferri-leakeite has a hardness in the range of 5-6 on the Mohs scale, which is typical for amphiboles. It has a density of approximately 3.23 g/cm³. It exhibits perfect cleavage in two directions, intersecting at angles of about 56 and 124 degrees, which is a characteristic feature of this mineral group. ## History and Name The mineral's name refers to its chemical composition – indicating the dominance of potassium (potassic) and trivalent iron (ferri) and its relation to other minerals of the leakeite group. It was formally described and approved by the International Mineralogical Association (IMA) as a distinct mineral species.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: Gray
Density: 3.23
Cleavage: Perfect on {110}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying potassic-ferri-leakeite based on visual features is practically impossible and requires advanced analytical techniques, such as X-ray microanalysis (EDS/WDS) or X-ray diffraction (XRD). A black color, prismatic habit, and co-occurrence with other rare alkaline minerals may be indicative. ## Distinguishing from Similar Minerals This mineral is indistinguishable to the naked eye from other black amphiboles, such as arfvedsonite, riebeckite, or other minerals from the sodic subgroup. Definitive differentiation is only possible based on chemical analysis, which will reveal a specific combination of potassium, sodium, magnesium, iron, and lithium. ## Crystal Forms It forms columnar or acicular crystals, often gathered in radial or fibrous aggregates. Crystals are usually small, not exceeding a few millimeters in length.

Geological environment

## Genesis Potassic-ferri-leakeite is a mineral of metamorphic origin. It forms under conditions of high-pressure regional metamorphism, in rocks such as marbles and gneisses, which are rich in sodium and potassium. ## Mineral Associations It co-occurs with minerals such as calcite, dolomite, quartz, albite, aegirine, titanite, apatite, and other rare amphiboles and pyroxenes. ## Localities The most important and best-documented locality for this mineral, which is also its type locality, is the Kajlidongri metamorphic complex in the Jhabua district, Madhya Pradesh, India. This is the only place from which well-studied specimens originate.

Rarity

Extremely rare

For collectors

## Quality Criteria As an extremely rare mineral, every analytically confirmed specimen has high scientific and collector value. The most desirable specimens are those with well-formed, visible crystals, set on a contrasting rock matrix (e.g., on white marble). Precise analytical documentation confirming the mineral's identity is important. ## Popular Localities The only source of collector specimens is the Kajlidongri manganese mine in India. Specimens from this locality are extremely difficult to acquire and are a highlight of advanced specialized collections (so-called systematic collections).

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. For heavier soiling, a soft, dry brush can be used. Avoid contact with water and chemical agents. ## What to Avoid Absolutely avoid contact with acids and other chemicals that may react with the mineral's components. As an amphibole group mineral, it may be sensitive to sudden temperature changes. Do not clean it with ultrasound. ## Storage Specimens, especially those with a fibrous structure, are brittle and susceptible to mechanical damage. It is best to store them in closed display boxes, lined with soft material, away from dust and direct sunlight.

Sources

IMA Mineral List (CNMNC)