Phosinaite-(Ce)

Chemical formula: Na₁₃Ca₂Ce₃+(SiO₃)₄(PO₄)₄

A sodium, calcium, and cerium silicate-phosphate, forming pinkish granular aggregates, found in alkaline pegmatites.

## Characteristics Fosinaite-(Ce) is a complex silicate-phosphate from the fosinaite group, in which cerium is the dominant rare earth element. This mineral most commonly occurs as massive, fine-grained, or coarse-grained aggregates. Well-formed crystals are extremely rare and usually appear as small, tabular or short-prismatic forms with poorly defined faces. Its appearance is typically inconspicuous, with the main visual feature being a delicate, pale pink or yellowish coloration. ## Physical Properties Fosinaite-(Ce) is a relatively soft mineral with a Mohs hardness of 3.5-4.5. It exhibits a vitreous luster on crystal surfaces and fractures. It is transparent to translucent. Its density ranges from 2.9-3.0 g/cm³. ## Colors and Varieties This mineral ranges in color from pale pink and pinkish-white to yellowish, and sometimes it can be colorless. There are no commercial names or colored varieties distinguished for it. ## History and Name The mineral's name, given in 1974 by a team of Russian mineralogists (Y.P. Menshikov, I.V. Bussen et al.), directly refers to its chemical composition: it contains **phos**phate (PO₄) groups, **si**licate groups, and **na**trium (sodium). The suffix "-(Ce)" indicates the dominance of cerium among the rare earth elements in its structure. ## Uses Fosinaite-(Ce) has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced collections of rare and systematic minerals.

Properties

Mohs hardness: 3.5-4.5
Luster: Vitreous
Streak: White
Density: 2.9-3.0
Cleavage: Good on {100}
Fracture: Uneven to conchoidal
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Helpful features for identifying fosinaite-(Ce) include its pale pink or yellowish color, vitreous luster, granular habit, and relatively low hardness. However, the key indicator is its specific environment of occurrence—strongly alkaline pegmatites and hydrothermal veins, and characteristic associated minerals. ## Distinguishing from Similar Minerals Fosinaite-(Ce) is sometimes confused with other pink minerals from the same environment, such as eudialyte or serandite. Eudialyte usually has a more intense, reddish-pink color and is harder (5-5.5). Serandite forms radiating aggregates of well-formed, prismatic crystals with a salmon hue and perfect cleavage. Definitive distinction often requires advanced chemical analysis. ## Crystal Forms Crystals are very rare, poorly formed, with tabular or short-prismatic habits. It is most commonly found as anhedral (unformed) grains forming massive, compact aggregates.

Geological environment

## Genesis Fosinaite-(Ce) is a characteristic mineral of highly differentiated, ultra-agpaitic (extremely alkaline) nepheline-syenite complexes. It forms during the late stages of crystallization, within pegmatites and hydrothermal veins, where sodium, rare earth elements, and other incompatible elements become concentrated. ## Mineral Associations This mineral co-occurs with a rich assemblage of other rare alkaline minerals, such as nepheline, microcline, aegirine, lomonosovite, sodalite, eudialyte, villiaumite, natrosilite, and rasvumite. ## Localities The most important and classic localities for fosinaite-(Ce) worldwide are the Khibiny Massif and Lovozero Massif on the Kola Peninsula in Russia. It is also known from another famous alkaline complex—Mont Saint-Hilaire in Quebec, Canada, although specimens from there are much rarer.

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized fosinaite-(Ce) specimens are those that show at least partially developed crystalline forms. Value is enhanced by the intensity of the pink color, a large aggregate surface, and attractive contrast with associated minerals, for example, with black aegirine or red eudialyte. Due to its rarity, even rich granular aggregates are sought after by collectors. ## Popular Localities The vast majority of the best collector specimens come from two Russian localities: Mount Rasvumchorr and Kedykvyrpakhk in the Khibiny Massif, and Mount Alluaiv and Karnasurt in the Lovozero Massif. Specimens from Mont Saint-Hilaire in Canada are also highly desirable, but are very rare on the market.

Care and storage

## Cleaning Fosinaite specimens should be cleaned very carefully, using a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they could damage the specimen due to its cleavage. ## What to Avoid The mineral is relatively soft and brittle, so it should be protected from impacts and contact with harder minerals. It is soluble in acids. All strong chemicals and sudden temperature changes should be avoided. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratching and mechanical damage. It is stable under normal household conditions.

Sources

IMA Mineral List (CNMNC)