Fluorcalciobritholite

Chemical formula: (Ca,REE)₅(SiO₄,PO₄)₃F

Fluorcalciobritholite is a rare mineral from the apatite group, being a silicate and phosphate of calcium and rare earth elements with fluorine.

## Characteristics Fluorcalciobritholite is a mineral belonging to the apatite supergroup. It occurs in the form of hexagonal, prismatic crystals, which can reach up to 2 cm in length, as well as in granular aggregates. It is usually opaque, with a vitreous or resinous luster. ## Physical Properties This mineral is characterized by a hardness of 5 on the Mohs scale. It is relatively brittle, and its fracture is uneven to conchoidal. The calculated density is approximately 4.23 g/cm³. ## Colors and Varieties Fluorcalciobritholite most often takes on a brown to reddish-brown color. No commercial or colored varieties have been distinguished. ## History and Name The mineral's name refers to its chemical composition – the dominance of fluorine (Fluor), calcium (calcio), and its similarity to britholite. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2005. The type locality from which it originates is the Khibiny Massif on the Kola Peninsula in Russia.

Properties

Mohs hardness
5.5
Color
Pinkish to brown
Luster
Vitreous to resinous
Streak
white
Density
4.2
Cleavage
Indistinct on {0001}
Fracture
Uneven to subconchoidal
Transparency
Transparent,Translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Key diagnostic features include the hexagonal habit of crystals, brown color, hardness of 5, and occurrence in a specific geological environment (alkaline massifs). Final confirmation requires advanced chemical analyses (EDS/WDS) to determine the composition, especially the content of calcium, rare earth elements, and fluorine. ## Distinguishing from Similar Minerals It can be confused with other minerals from the apatite group, such as britholite-(Ce) or fluorapatite. Differentiation is possible almost exclusively based on detailed chemical composition studies, as physical properties and appearance are very similar. ## Crystal Forms Most often, it forms elongated, prismatic crystals with a hexagonal outline. It also occurs as irregular granular aggregates in the host rock.

Geological environment

## Genesis Fluorcalciobritholite forms in highly differentiated, alkaline magmatic complexes, particularly in nepheline syenites and associated pegmatites. It is a mineral of the late stage of magmatic crystallization. ## Mineral Associations It often co-occurs with minerals typical of alkaline pegmatites, such as nepheline, microcline, eudialyte, lorenzenite, lamprophyllite, aegirine, and astrophyllite. ## Localities The most important and well-documented locality, which is also the type locality, is the Khibiny Massif on the Kola Peninsula in Russia. Other confirmed occurrences include the Ilímaussaq complex in Greenland and the Lovozero Massif, also on the Kola Peninsula.

Rarity

Very rare

For collectors

## Quality Criteria The most valuable specimens for collectors are those with well-formed, sharp, and undamaged crystals of a distinct, hexagonal shape. Specimens where fluorcalciobritholite crystals are embedded in a contrasting rock matrix, accompanied by other rare minerals such as eudialyte or astrophyllite, are also prized. The intensity and uniformity of color also influence the specimen's attractiveness.

Care and storage

## Cleaning It is recommended to clean specimens only with compressed air or a very soft brush to remove dust. Avoid contact with water and chemical agents. ## What to Avoid The mineral is brittle and sensitive to impact. Avoid contact with acids and other chemicals that may damage its surface. Do not heat it or subject it to ultrasound. ## Storage Specimens should be stored in separate, padded boxes to prevent scratches and mechanical damage. Protect from dust and moisture.

External references

Sources

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