IMA2009-079

Chemical formula: KNa₂(Mg₄Fe₃+)Si₈O₂₂F₂

Ferro-fluoro-leakeite is a very rare, dark green to black amphibole group mineral, discovered in the Altai Mountains in China.

## Characteristics Ferro-fluoro-leakeite is a complex silicate belonging to the amphibole supergroup. It forms elongated, prismatic crystals, typically up to 1 mm long, which occur as aggregates or individually within the host rock. Its color ranges from dark green to almost black, and it appears green when translucent on thin edges. It is an opaque mineral. ## Physical Properties The mineral is characterized by a hardness of 5-6 on the Mohs scale. It has a vitreous luster and a greenish-gray streak. The density calculated from crystallographic data is approximately 3.23 g/cm³. ## History and Name The mineral was first identified in material from the Kökbota Complex, in the Chinese part of the Altai Mountains. Its discovery was approved by the International Mineralogical Association (IMA) in 2009 under the provisional designation IMA2009-079. The name "ferro-fluoro-leakeite" refers to its chemical composition – the dominance of iron (ferro) and fluorine (fluoro) – and its relation to leakeite, another amphibole group mineral named after Bernard E. Leake, a British geologist and amphibole researcher.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: Greenish-gray
Density: 3.23
Cleavage: Good on {110}
Fracture: Uneven
Transparency: Opaque, translucent on edges
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of ferro-fluoro-leakeite requires advanced analytical techniques, such as electron microprobe (EDS/WDS) and X-ray diffraction (XRD), due to its similarity to other dark amphiboles. For collectors, identification is primarily based on the label from a confirmed locality. ## Distinguishing from Similar Minerals It can be confused with other amphiboles, such as hornblende, arfvedsonite, or other minerals from the leakeite subgroup. Definitive differentiation is only possible through detailed chemical analysis, which will show the dominance of iron over magnesium and fluorine over hydroxyl groups. ## Crystal Forms Crystals are prismatic, elongated along the crystallographic c-axis, and reach up to 1 mm in length and 0.2 mm in width. They occur as single crystals or radial aggregates.

Geological environment

## Genesis Ferro-fluoro-leakeite forms under conditions of high-pressure metamorphism. It has been found in eclogite rocks that underwent retrogression in the greenschist facies. Its presence is associated with alkaline metasomatism rich in fluorine. ## Mineral Associations This mineral co-occurs with minerals such as albite, crossite, aegirine, quartz, titanite, apatite, zircon, hematite, and rare fluoro-arfvedsonite. ## Localities The only confirmed occurrence (type locality) is the Kökbota metamorphic complex in the western Altai Mountains region, Xinjiang autonomous region, China.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" mineral, its collector value depends on the quality and size of the crystals, their habit, and the richness of the aggregate on the rock matrix. The most desirable specimens are those with well-defined, undamaged prismatic crystals that stand out clearly from the rock background. Association with other rare minerals is also important. ## Popular Localities The only source of specimens is the type locality in China, which makes every specimen from there extremely valuable for collectors specializing in mineral systematics or rare minerals.

Care and storage

## Cleaning Due to its rarity and potential fragility, only gentle cleaning with compressed air or a very soft brush is recommended to remove dust. Avoid contact with water and chemical agents. ## What to Avoid Avoid ultrasonic cleaners, sudden temperature changes, and all acids and solvents, which could damage delicate crystals or react with the mineral. ## Storage Specimens should be stored in stable conditions, away from direct sunlight and moisture. The safest solution is to place them in a sealed "micromount" box to protect them from mechanical damage and dust.