Fluocerite-(La)

Chemical formula: La³⁺F₃

Fluocerite-(La) is a rare lanthanum fluoride, forming hexagonal crystals with a waxy or vitreous luster, prized by collectors of rare earth minerals.

## Characteristics Fluocerite-(La) is a lanthanum fluoride belonging to the group of rare earth minerals. It occurs as hexagonal, tabular, or prismatic crystals, often terminated by pyramids. Specimens can also be massive or granular. Its surface is usually dull or covered with weathering products, but fresh fractures reveal a waxy to vitreous luster. ## Physical Properties This mineral is characterized by a hardness of 4-5 on the Mohs scale. It is brittle, and its fracture is uneven. It does not exhibit cleavage. Its density has not been precisely determined but is estimated at approximately 5.93 g/cm³. ## Colors and Varieties Fluocerite-(La) most commonly ranges in color from yellow, through yellowish-brown, reddish-brown, to almost black. The coloration is often non-uniform. No named varieties of this mineral are distinguished. ## History and Name The name "fluocerite" refers to its chemical composition (fluorine and cerium, which is related to lanthanum in the lanthanide group) and was first used in 1838. The suffix "-(La)" was added later, in accordance with mineral nomenclature rules, to indicate that lanthanum is dominant in this specific mineral. The mineral was described based on specimens from the Zhanuzak deposit in Kazakhstan, which is its type locality.

Properties

Mohs hardness
4-5
Luster
Vitreous to Waxy
Streak
White to yellowish white
Density
0
Fracture
Uneven
Transparency
Translucent to Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Key diagnostic features include the hexagonal crystal shape, relatively low hardness (it can be scratched with a knife), waxy luster on a fresh fracture, and high density (the specimen feels heavy for its size). Occurrence in granitic pegmatites or carbonatites in association with other rare earth minerals is also a strong indicator. ## Distinguishing from Similar Minerals Fluocerite-(La) can be confused with other rare earth minerals such as bastnäsite or monazite. Bastnäsite has similar colors and forms but is slightly harder and often exhibits a more pronounced luster. Monazite crystallizes in the monoclinic system, and its crystals have a different shape. Precise differentiation of these minerals often requires advanced chemical analysis (EDS). ## Crystal Forms Crystals are typically hexagonal, with a tabular or short-prismatic habit. They often form granular aggregates or massive masses. Well-formed, single crystals are rarer.

Geological environment

## Genesis Fluocerite-(La) is a mineral of magmatic origin. It forms in the late stages of crystallization of granitic pegmatites, especially those enriched in rare earth elements. It is also found in some carbonatites and hydrothermal veins. ## Mineral Associations It often co-occurs with other rare earth minerals such as bastnäsite, cerite, allanite, monazite, as well as with quartz, microcline, albite, and fluorite. ## Localities The most important localities worldwide include the type locality Zhanuzak in Kazakhstan, as well as pegmatites in the Österby area in Sweden, the Urals in Russia, and some localities in the USA (e.g., Colorado).

Rarity

Very rare

For collectors

## Quality Criteria Collectors most seek specimens with well-formed, sharp, and undamaged hexagonal crystals. Specimens with intense yellow or brown coloration are also valued. An aesthetic composition with other minerals, such as contrasting fluocerite crystals on light quartz or feldspar, is also important. ## Popular Localities Specimens from classic, historic localities in Sweden (e.g., Österby, Finnbo) are highly prized due to their scientific significance. Good quality crystals also come from some pegmatites in Russia and Kazakhstan.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush or compressed air to remove dust. Due to its brittleness and potential reactivity, contact with water and chemical agents should be avoided. ## What to Avoid Avoid contact with acids and other chemicals that may damage the mineral's surface. It should not be heated or subjected to ultrasound. Prolonged exposure to moisture can lead to its slow decomposition. ## Storage It is recommended to store fluocerite-(La) under stable conditions, in a dry environment, away from direct sunlight and heat sources. It is best kept in a closed display box to protect it from dust and mechanical damage.

External references

Sources

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