Arrheniusite-(Ce)

Chemical formula: CaMg[(Ce₃+₇Y₃)Ca₅](SiO₄)₃(Si₃B₃O₁₈)(As₅+O₄)(BO₃)F₁₁

Arrheniusite-(Ce) is an extremely rare mineral from the gadolinite group, characterized by its exceptionally complex chemical composition and occurrence as small, black masses.

## Characteristics Arrheniusite-(Ce) is a mineral with an exceptionally complex chemical structure, belonging to the gadolinite group. It occurs as anhedral (irregularly formed) grains and aggregates up to 1 cm in size. Its black, opaque form and pitchy luster are characteristic visual features. This mineral is brittle and exhibits an uneven fracture. ## Physical Properties Arrheniusite-(Ce) has a Mohs hardness of 5.5. Its luster is described as pitchy to vitreous. It is an opaque mineral. The density calculated based on the chemical formula and unit cell parameters is 4.67 g/cm³. ## Colors and Varieties This mineral occurs in a uniform, black color. No color varieties or commercial forms are known. ## History and Name The mineral's name honors Carl Axel Arrhenius (1757–1824), a Swedish chemist and mineralogist who was the first to discover rare earth minerals in the Ytterby pegmatites in Sweden. The suffix "-(Ce)" refers to the dominant rare earth element in its composition – cerium. The mineral was officially recognized by the International Mineralogical Association (IMA) in 2002. ## Uses Due to its extreme rarity, Arrheniusite-(Ce) has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors.

Properties

Mohs hardness: 5.5
Luster: Resinous to Vitreous
Streak: Brown
Density: 4.67
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identifying Arrheniusite-(Ce) in the field is practically impossible without advanced analytical techniques. In a collection, it can be provisionally identified based on its black color, pitchy luster, uneven fracture, and most importantly, a confirmed origin locality (Östanmossa mine, Sweden). Final identification requires chemical analysis (EDS/WDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals This mineral can be confused with other black, massive minerals from pegmatites, such as gadolinite, allanite, euxenite, or fergusonite. Differentiation relies solely on detailed chemical composition and crystal structure analysis. Arrheniusite-(Ce) is distinguished by a unique combination of silicon, boron, and arsenic in its structure. ## Crystal Forms Arrheniusite-(Ce) occurs as anhedral (xenomorphic) grains and aggregates. No well-formed crystals have been observed.

Geological environment

## Genesis Arrheniusite-(Ce) forms in granitic skarn pegmatites that are enriched in rare earth elements. It is a late-stage crystallization mineral under very specific geochemical conditions. ## Mineral Associations This mineral co-occurs with other minerals typical of skarn pegmatites, such as diopside, titanite, fluorite, fluocerite-(Ce), bastnäsite-(Ce), törnebohmit-(Ce), gadolinite-(Y), and danalite. ## Localities The only confirmed locality for Arrheniusite-(Ce) in the world is its type locality – the Östanmossa mine in Norberg Municipality, Västmanland region, Sweden.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an Arrheniusite-(Ce) specimen is primarily determined by its size and abundance within the host rock. Since this mineral does not form aesthetic crystals, the most valued specimens are the largest, pure fragments or aggregates, clearly visible in association with other minerals from this locality. The certainty of identification, confirmed by analysis, is also crucial. ## Popular Localities The only source of Arrheniusite-(Ce) specimens is the Östanmossa mine in Sweden. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Due to its brittleness and rarity, cleaning should be limited to an absolute minimum. If necessary, a soft brush can be used to remove dust. Water and any chemical agents should be avoided. ## What to Avoid Contact with acids and other chemicals that may react with the mineral's complex composition must be strictly avoided. It should be protected from ultrasound, high temperatures, and sudden temperature changes. The mineral is brittle, so impacts and drops should be avoided. ## Storage Specimens of Arrheniusite-(Ce) should be stored in stable conditions, in a separate, padded collector's box to prevent abrasions and mechanical damage. It should be protected from dust and moisture.

Sources

IMA Mineral List (CNMNC)