Fluocerite-(Ce)

Chemical formula: Ce<sup>3+</sup>F<sub>3</sub>

Fluocerite-(Ce) is a rare cerium fluoride, forming hexagonal crystals with a characteristic reddish-brown or yellow color and a resinous luster.

## Characteristics Fluocerite-(Ce) is a mineral from the halide group, consisting mainly of fluorine and cerium. It occurs in the form of hexagonal, tabular or short-prismatic crystals, often imperfectly formed. It usually forms massive, granular, or embedded aggregates within the host rock. Its surfaces can be dull or covered with weathering products. ## Physical Properties This mineral is relatively soft, with a Mohs hardness ranging from 4 to 5. It is brittle and quite heavy, with a density reaching up to 6.1 g/cm³. It is characterized by a resinous, somewhat greasy luster on fresh fracture surfaces. It is translucent to opaque. ## Colors and Varieties The most common colors are reddish-brown, waxy yellow, yellowish-brown, and brown. The color is usually uniform, although external surfaces may be altered due to weathering processes. No commercial or color varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – the presence of fluorine (Latin: *fluo* - to flow) and the dominant rare-earth element, cerium (Ce). It was first described in 1845 based on specimens found in the Bastnäs mines in Sweden. The suffix "-(Ce)" was added in 1987 by the International Mineralogical Association (IMA) to precisely indicate the dominant rare-earth element in its structure, in accordance with Levinson's rule.

Properties

Mohs hardness
4-5
Luster
Resinous to vitreous
Streak
White to yellowish-white
Density
5.93-6.1
Cleavage
Good on {0001}, imperfect on {1120}
Fracture
Uneven to subconchoidal
Transparency
Translucent to opaque
Crystal system
Trigonal

Diagnostic features

## Identification Characteristic features of fluocerite-(Ce) include its trigonal (hexagonal) crystal form, resinous luster, relatively high density, and typical reddish-brown or yellow coloration. It is one of the few simple rare-earth fluorides. ## Distinguishing from Similar Minerals It can be confused with bastnäsite-(Ce), with which it often co-occurs. However, bastnäsite is usually more transparent, has a vitreous luster, and higher hardness (4.5-5). Differentiation in granular aggregates can be difficult and often requires chemical analysis (XRD/EDS). From other minerals of similar color (e.g., some garnets), it is distinguished by its lower hardness and crystal form. ## Crystal Forms Crystals have a tabular or thick-tabular habit, less commonly prismatic, with a hexagonal outline. They often occur as embedded, imperfectly formed individuals or in the form of granular aggregates and masses filling spaces in the rock.

Geological environment

## Genesis Fluocerite-(Ce) is a mineral of magmatic origin, crystallizing in the late stages from granitic and syenitic pegmatites rich in rare-earth elements. It also forms in hydrothermal processes, in quartz veins cutting alkaline rocks. ## Mineral Associations It often co-occurs with other rare-earth minerals such as bastnäsite-(Ce), cerite-(Ce), allanite-(Ce), monazite-(Ce), as well as with quartz, fluorite, thorite, and various amphiboles. ## Localities The most important historical localities are in the Bastnäs area, Västmanland, Sweden. Other known localities include Pikes Peak in Colorado (USA), where it occurs in pegmatites, as well as in the Urals in Russia and in Norway.

Rarity

Rare

For collectors

## Quality Criteria The most sought-after by collectors are well-formed, sharp, hexagonal crystals with an intense, uniform color and good luster. Specimens where fluocerite-(Ce) is deposited on a contrasting rock matrix or co-occurs with other rare minerals, such as bastnäsite, are particularly valuable. Crystal size is also a key factor – larger, well-formed specimens are rare.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Due to its reactivity, contact with water, especially acids, should be avoided. ## What to Avoid All chemicals, including acids and strong bases, which can damage or completely destroy the mineral, must be absolutely avoided. Fluocerite-(Ce) is sensitive to moisture and can undergo alterations upon contact with water. It should be protected from high temperatures and sudden temperature changes. ## Storage It is recommended to store it in a dry place, preferably in an airtight container or a display box away from other minerals that could scratch it. Exposure to humid air should be avoided.

Sources

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