Fluormacraeite

Chemical formula: [(H<sub>2</sub>O)K]Mn<sup>2+</sup><sub>2</sub>(Fe<sup>3+</sup><sub>2</sub>Ti<sup>4+</sup>)(PO<sub>4</sub>)<sub>4</sub>(OF)(H<sub>2</sub>O)<sub>10</sub>·4H<sub>2</sub>O

Fluormacraeite is a newly discovered, extremely rare phosphate mineral of the macraeite group, distinguished by its complex chemical composition and occurrence in a unique geological environment.

## Characteristics Fluormacraeite is a mineral ranging in color from yellow to orange-brown, forming aggregates of platy or bladed crystals. Individual crystals are very small, reaching up to 200 micrometers in length and only a few micrometers thick. These aggregates typically have a radial or tangled structure. The mineral is translucent and exhibits a vitreous luster. ## Physical Properties Due to the microscopic size of the crystals, precise determination of hardness and density was not possible. Hardness is estimated to be around 2 on the Mohs scale, which is typical for minerals with a similar structure. The mineral exhibits perfect cleavage in one direction, corresponding to its platy habit. It does not show fluorescence under ultraviolet light. ## History and Name Fluormacraeite was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2023 (IMA2023-088). Its name refers to the dominance of fluorine in its chemical composition and its structural relationship to the mineral macraeite. It was discovered at the Foote Lithium Co. quarry in North Carolina, USA, which is its only known locality.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Light yellow
Cleavage
Perfect on {001}
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Identification of fluormacraeite is possible only through advanced analytical methods, such as energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD), due to its microscopic size and rarity. Visually, it appears as fine, yellow-orange, radial aggregates of platy crystals on the matrix. ## Distinguishing from Similar Minerals It can be confused with other secondary phosphate minerals found in the same locality, such as strengite, rockbridgeite, or other minerals of the macraeite group. Definitive differentiation requires specialized chemical analysis to confirm its unique composition with the presence of potassium, titanium, and fluorine. ## Crystal Forms It forms thin, platy or bladed crystals that combine into radial, spherical, or tangled aggregates. Single, well-formed crystals are extremely rare and visible only under high magnification.

Geological environment

## Genesis Fluormacraeite forms as a secondary mineral in complex lithium- and phosphorus-rich granitic pegmatites. It crystallizes in the late stage of hydrothermal processes, as a result of the alteration of earlier phosphate minerals in the presence of fluorine-rich solutions. ## Mineral Associations This mineral coexists with quartz, microcline, albite, strengite, rockbridgeite, zincian strengite, switzerite, and other rare phosphates. ## Localities The only confirmed occurrence of fluormacraeite in the world is the Foote Lithium Co. quarry in Cleveland County, North Carolina, USA. This is the type locality for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" mineral, its collector value depends on the richness and aesthetics of the aggregates on the matrix. The most prized specimens are those with distinct, well-formed radial clusters of intense orange color, contrasting with the substrate. The presence of associated minerals is also important. ## Popular Localities The only source of specimens is the historically important Foote quarry in North Carolina, known to collectors for its many rare and unique minerals. Fluormacraeite specimens from this locality are highly sought after by specialized collectors of rare and "micromount" minerals.

Care and storage

## Cleaning Due to its extreme rarity, small size, and fragility, fluormacraeite specimens should not be cleaned mechanically or chemically. Any attempts at cleaning may irreversibly damage the mineral. It should be left undisturbed on its matrix. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and any tools. The mineral is very soft and brittle. It should be protected from vibrations, shocks, and sudden temperature changes. ## Storage Specimens should be stored exclusively in specialized, sealed "micromount" boxes, protecting them from dust, moisture, and mechanical damage. Display should only occur under a microscope, away from direct sunlight and heat sources.

Sources

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