Fluoro-magnesiokatophorite

Chemical formula: NaCa₂Mg₅(Si₇Al)O₂₂F₂

Fluoro-magnesio-katophorite is a very rare mineral from the amphibole group, characterized by a dark green or black color and the presence of fluorine in its structure.

## Characteristics Fluoro-magnesio-katophorite is a complex silicate from the amphibole supergroup, belonging to the katophorite series. It typically forms small, prismatic crystals of dark green, greenish-black, or black color. It is an opaque mineral or only translucent on thin edges. It is the fluorine and magnesium analogue of other minerals in this group. ## Physical Properties The mineral is characterized by a vitreous luster. Its calculated density is approximately 3.19 g/cm³. The hardness has not been precisely measured, but for amphiboles, it generally falls within the range of 5-6 on the Mohs scale. It exhibits good cleavage in two directions, typical for amphiboles. ## Colors and Varieties Observed colors are limited to dark shades of green and black. Due to its rarity, no colored or commercial varieties have been distinguished. ## History and Name The mineral's name directly reflects its chemical composition: the prefix "fluoro-" indicates the dominance of fluorine over hydroxyl groups, "magnesio-" indicates the dominance of magnesium, and "katophorite" defines its belonging to the appropriate series within amphiboles. It was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2012. ## Applications Fluoro-magnesio-katophorite has no industrial applications. Its significance is purely scientific and collectible, as a very rare member of the large and complex amphibole group.

Properties

Luster: Vitreous
Streak: White
Density: 3.19
Cleavage: Good on {110}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Field identification is practically impossible. The dark color, prismatic habit, and vitreous luster are typical of many amphiboles. A key clue is the environment of occurrence – calc-silicate rocks within marbles. Certain identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS) to confirm the chemical composition rich in fluorine, magnesium, sodium, and calcium. ## Distinguishing from Similar Minerals Fluoro-magnesio-katophorite is visually indistinguishable from other dark amphiboles, such as hornblende, arfvedsonite, or other minerals from the katophorite group. The differences between them are chemical in nature and require specialized research equipment for determination. ## Crystal Forms This mineral forms elongated, columnar, or prismatic crystals, often occurring as radial or disordered aggregates embedded in the host rock.

Geological environment

## Genesis Fluoro-magnesio-katophorite is a metamorphic mineral. It forms under conditions of contact metamorphism, in calc-silicate rocks (skarns) formed within Proterozoic marbles. Its crystallization requires a fluorine-rich environment. ## Mineral Associations At the type locality, it coexists with minerals such as diopside, calcite, phlogopite, fluorite, and zircon. ## Localities The only confirmed locality of this mineral in the world is its type locality – the Greenwood area (near the old Parker Mine) in Orange County, New York, USA.

Rarity

Very rare

For collectors

## Quality Criteria As a mineral occurring mainly in the form of microcrystals, its collector's value primarily depends on the degree of crystal development and sharpness. Specimens with distinct, undamaged prisms, ideally contrasting with the light background of the host rock (matrix), are most highly prized. The presence of well-formed associated minerals also enhances its attractiveness. ## Popular Localities All material available on the collector's market comes from a single location in the world: the Greenwood area in New York State, USA. Specimens from this locality are sought after by specialized collectors of rare minerals and microminerals.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush or compressed air to remove dust. Distilled water may be used, but prolonged soaking should be avoided. Ultrasonic cleaners are not recommended due to the risk of damage along cleavage planes. ## What to Avoid The mineral is sensitive to strong acids, especially hydrofluoric acid. It should be protected from sudden temperature changes and prolonged exposure to direct sunlight, which may slightly affect its appearance. ## Storage It is recommended to store specimens in closed display cases or boxes to protect them from dust and mechanical damage. It is best kept under stable humidity and temperature conditions, away from heat sources.

Sources

IMA Mineral List (CNMNC)