Fluoro-ferri-magnesiokatophorite

Chemical formula: Na₂Ca(Mg,Fe₃+)₅(Si₇Al)O₂₂F₂

A rare amphibole from the katophorite group, distinguished by the presence of fluorine and trivalent iron in its chemical structure.

## Characteristics Fluoro-ferri-magnesiokatophorite is a complex silicate belonging to the amphibole group. It is an extremely rare mineral, identified based on microscopic analyses. It occurs as fibrous or prismatic crystals of submillimeter size, usually forming aggregates. Due to its rarity and microscopic nature, a full visual description of macroscopic specimens is not well documented. ## Physical Properties As a member of the amphibole group, it exhibits typical characteristics. Its Mohs hardness is approximately 6. The mineral is characterized by a vitreous luster. It is translucent to opaque. The density calculated from the formula and cell parameters is approximately 3.23 g/cm³. ## Colors and Varieties Observed crystals range in color from light brown to reddish-brown. No named varieties of this mineral have been distinguished. ## History and Name The mineral's name directly refers to its chemical composition and its relationship with other minerals from the katophorite group. The prefix "Fluoro" indicates the dominance of fluorine over the hydroxyl group, "ferri" denotes the presence of iron in the trivalent state (Fe³⁺), and "magnesio" signifies the dominance of magnesium. It was formally described and approved by the International Mineralogical Association (IMA) in 2013 (IMA2013-076).

Properties

Mohs hardness: 6
Luster: Vitreous
Streak: Light brown
Density: 3.23
Cleavage: Perfect on {110}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of Fluoro-ferri-magnesiokatophorite is impossible without advanced analytical techniques. This requires the use of an electron microprobe (for chemical composition analysis) and single-crystal X-ray diffraction (to determine the structure). In optical studies under a polarizing microscope, it exhibits pleochroism in shades of brown. ## Distinguishing from Similar Minerals This mineral is visually indistinguishable from other amphiboles of the katophorite group, such as magnesiokatophorite or ferrikatophorite. The only way to differentiate them is through precise chemical analysis, which allows for the determination of dominant elements in specific structural positions (e.g., dominance of fluorine over the OH group, magnesium over Fe²⁺, and the presence of Fe³⁺). ## Crystal Forms It forms elongated, prismatic, or fibrous crystals, typically not exceeding 0.2 mm in length. They occur as aggregates or inclusions within other rock-forming minerals.

Geological environment

## Genesis Fluoro-ferri-magnesiokatophorite forms under conditions of high-pressure and high-temperature metamorphism. Its occurrence is associated with metamorphic rocks, such as eclogites. ## Mineral Associations This mineral coexists with other minerals typical of high-grade metamorphic rocks. In its type locality (Sesia-Lanzo, Italy), it was found in association with omphacite, garnet (almandine-grossular), quartz, rutile, apatite, talc, dolomite, titanite, and zircon. ## Localities The only confirmed occurrence of this mineral worldwide is its type locality: the Sesia-Lanzo Zone in the Western Alps, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria As a mineral of purely scientific importance and occurring in microscopic form, it is not subject to standard collector evaluation criteria such as size, color, or clarity. The scientific value of a specimen depends on its analytical quality and the accurate documentation of coexisting minerals. ## Market Prices This mineral is not traded on the collector's market. ## Popular Localities The only known locality is the type locality in Italy, which is not a source of collector specimens in the common sense.

Care and storage

## Cleaning Due to its microscopic nature and extreme rarity, specimens of this mineral (usually in the form of polished thin sections for research) should not be cleaned by collectors. Any conservation activities should be left to specialized laboratories. ## What to Avoid Avoid contact with any chemicals, especially strong acids, which can react with silicates. Also, avoid ultrasound and sudden temperature changes. ## Storage Research specimens should be stored under stable laboratory conditions, in special containers protecting them from dust, moisture, and mechanical damage.

Sources

IMA Mineral List (CNMNC)