Ferri-leakeite

Chemical formula: NaNa<sub>2</sub>(Mg<sub>2</sub>Fe<sup>3+</sup><sub>2</sub>Li)Si<sub>8</sub>O<sub>22</sub>(OH)<sub>2</sub>

Ferri-leakeite is a rare, dark-green to black amphibole group mineral, forming prismatic crystals in metamorphic rocks.

## Characteristics Ferri-leakeite is a complex silicate from the amphibole supergroup, belonging to the sodic amphibole group. It forms elongated, prismatic crystals, often occurring as radial or subparallel aggregates. Its color is characteristic, ranging from dark green to almost black, which is associated with a high content of ferric iron (Fe³⁺) in its structure. Specimens are usually opaque, becoming translucent only in thin fragments. ## Physical Properties The hardness of ferri-leakeite on the Mohs scale is 5-6, which is typical for amphiboles. This mineral is characterized by a vitreous luster. It has good cleavage in two directions, intersecting at angles of approximately 56° and 124°, which is a diagnostic feature for the entire amphibole group. Its density is about 3.23 g/cm³. ## Colors and Varieties This mineral occurs in uniform, dark colors – from dark green to black. No color varieties or commercial varieties are distinguished. ## History and Name Ferri-leakeite was described and recognized as a new mineral species in 1992 by a team of mineralogists led by Frank C. Hawthorne. Its name refers to the dominant ferric iron (ferri) in its composition and its structural relationship to leakeite, another mineral from the same group. The type locality (locus typicus) is the Kajlidongri mine in the Jhabua district, Madhya Pradesh state, India. ## Applications Ferri-leakeite has no industrial applications. It is a mineral of interest and sought after exclusively by collectors of rare minerals and specialists.

Properties

Mohs hardness
5-6
Luster
Vitreous
Streak
Pale green
Density
3.23
Cleavage
Good on {110}
Fracture
Splintery
Transparency
Translucent to Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Key features for identifying ferri-leakeite are its dark green to black color, prismatic crystal habit, and amphibole-typical cleavage. Its occurrence environment – metamorphosed manganese deposits – is also an important indicator. ## Distinguishing from Similar Minerals Ferri-leakeite can be confused with other dark amphiboles, such as arfvedsonite, riebeckite, or hornblende. Reliable differentiation based on visual characteristics is very difficult and most often requires advanced chemical analyses (e.g., electron microprobe) to confirm high ferric iron and lithium content. ## Crystal Forms Crystals are most often elongated, prismatic, with a hexagonal or octagonal cross-section. They usually form fan-shaped, radial, or chaotically arranged aggregates. Less commonly, they occur as single, well-formed crystals.

Geological environment

## Genesis Ferri-leakeite is a mineral of metamorphic origin. It forms under regional metamorphic conditions in rocks rich in sodium and manganese. ## Mineral Associations This mineral co-occurs with other minerals characteristic of metamorphosed manganese deposits. In the type locality (Kajlidongri), these include braunite, bixbyite, jacobsite, aegirine, spessartine, and quartz. ## Localities The most important and globally known locality for ferri-leakeite, from which the best collector specimens originate, is the Kajlidongri mine in Madhya Pradesh state, India. Other, much rarer occurrences have been reported in Sweden (Långban mine), among others.

Rarity

Rare

For collectors

## Quality Criteria The most highly prized ferri-leakeite specimens are those consisting of well-formed, sharp, and lustrous crystals, forming aesthetic, radial aggregates. The value is enhanced by a contrasting rock matrix and the presence of well-formed associated minerals, e.g., braunite. Crystal size is also an important factor. ## Popular Localities Virtually all ferri-leakeite specimens available on the collector's market come from a single location – the Kajlidongri mine in India. This is the classic locality for this mineral.

Care and storage

## Cleaning Ferri-leakeite specimens should be cleaned carefully, using a soft brush and distilled water. Due to the possible presence of fragile, acicular aggregates, strong rubbing should be avoided. ## What to Avoid The mineral is sensitive to strong acids. Ultrasonic cleaners are not recommended, as vibrations can damage delicate crystal aggregates. It is stable under normal temperature conditions and is not sensitive to light. ## Storage Collectible ferri-leakeite specimens should be stored in separate boxes or in a way that prevents contact with harder minerals (e.g., quartz) to avoid scratches. It does not require special humidity conditions.

Sources

Read more