Fluorcarletonite

Chemical formula: KNa₄Ca₄Si₈O₁₈(CO₃)₄F·H₂O

Fluorcarletonite is an extremely rare silicate, a fluorine analogue of carletonite, distinguished by its unique blue color.

## Characteristics Fluorcarletonite is a mineral from the silicate class, belonging to the apophyllite group. It is the fluorine analogue of carletonite, from which it differs by the dominance of fluorine over the hydroxyl group in its structure. It forms tabular or short-prismatic crystals, often grouped into blocky aggregates. Its most characteristic feature is an intense blue color, which can take on various shades – from light blue to azure and sapphire. The mineral can be partially or completely pseudomorphed after pectolite crystals. ## Physical Properties Crystals exhibit a hardness of approximately 4 on the Mohs scale, making them relatively soft and susceptible to scratching. The luster is vitreous, and on perfect cleavage planes, it becomes pearly. The mineral is transparent to translucent. Its density is approximately 2.42 g/cm³. ## Colors and Varieties The dominant and only known color of fluorcarletonite is blue, in a wide range of shades. Variability in color saturation within a single crystal or aggregate is common, creating visually attractive patterns. No named varieties are distinguished. ## History and Name Fluorcarletonite was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2019. Its name refers to two facts: it is an analogue of carletonite, in which fluorine (Latin: *fluere* - to flow) dominates the anionic position. The name of the parent mineral, carletonite, honors Carleton University in Ottawa (Canada), where it was first studied. ## Applications Due to its extreme rarity, fluorcarletonite has no industrial applications. It is solely an object of immense collector's value.

Properties

Mohs hardness: 4
Luster: Vitreous, pearly on cleavage planes
Streak: White
Density: 2.42
Cleavage: Perfect on {001}, good on {100}
Fracture: Uneven to conchoidal
Transparency: Transparent to translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Key identifying features of fluorcarletonite are its unique, intensely blue color, tetragonal crystal form, perfect cleavage in one direction, and pearly luster on the cleavage surfaces. Its origin from the only known locality in the world is also characteristic. ## Distinguishing from Similar Minerals Fluorcarletonite is visually indistinguishable from carletonite. The only reliable method of identification is advanced chemical analysis (e.g., electron microprobe), which confirms the dominance of fluorine over hydroxyl groups. From other blue minerals, such as lazurite or sodalite, it is distinguished by its lower hardness and perfect cleavage. ## Crystal Forms Crystals are tetragonal, most often in the form of tablets or short, prismatic columns. They usually occur as compressed, granular, or blocky aggregates, often forming pseudomorphs after other minerals, which gives them an irregular external shape.

Geological environment

## Genesis Fluorcarletonite forms under unique geological conditions, within highly alkaline potassic rocks. Its formation is associated with metasomatic processes occurring at the contact of syenite intrusions with surrounding carbonate rocks or within xenoliths of sedimentary rocks. ## Mineral Associations This mineral co-occurs with other rare minerals typical of the Murun Massif. The most common associations include microcline, quartz, pectolite, charoite, tinaksite, miserite, and frankamenite. ## Localities The only confirmed locality of fluorcarletonite in the world is the Murun Massif in the Irkutsk Oblast and Yakutia (Sakha Republic) in Siberia, Russia. This is the type locality for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly prized fluorcarletonite specimens are characterized by a deep, evenly distributed, sapphire-blue color. Large, well-formed crystals with strong luster are extremely rare and sought after. The aesthetic appeal of a specimen is also enhanced by attractive associations with contrasting minerals, such as white pectolite or purple charoite. ## Popular Localities All specimens available on the collector's market come from a single location – the Murun Massif in Russia. This is the only source of this mineral, making each specimen geographically unique.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, they can be quickly rinsed in distilled water and immediately and thoroughly dried. Ultrasonic cleaners should be avoided, as they can damage the mineral along cleavage planes. ## What to Avoid The mineral is sensitive to acids, which cause it to effervesce violently due to its carbonate content. It should be protected from high temperatures, which can lead to water loss from its structure and changes in properties. Due to its relatively low hardness and perfect cleavage, specimens are susceptible to mechanical damage and scratching. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to avoid contact with harder minerals. They should be protected from dust, humidity, and direct, prolonged exposure to sunlight, which could theoretically affect their color.

Sources

IMA Mineral List (CNMNC)