Graulichite-(Ce)

Chemical formula: Ce₃+Fe₃+₃(As₅+O₄)₂(OH)₆

A very rare cerium and iron arsenate from the alunite supergroup, forming microscopic, yellow rhombohedral crystals.

## Characteristics Graulichite-(Ce) is a rare secondary mineral belonging to the beudantite group within the alunite supergroup. It forms very small, usually microscopic crystals not exceeding 0.1 mm in size. They take the form of rhombohedra or pseudocubes. It also occurs as earthy or powdery coatings and aggregates. Its small size makes it a mineral of interest mainly to micromineralogy collectors. ## Physical Properties The mineral is characterized by a vitreous to resinous luster. It is translucent to opaque. Hardness has not been directly measured but is calculated to be approximately 4 on the Mohs scale, which is typical for minerals in its group. The calculated density is 4.35 g/cm³. ## Colors and Varieties The typical color of graulichite-(Ce) is yellow, transitioning to yellowish-brown hues. No color varieties or commercial varieties are distinguished. ## History and Name The mineral is named in honor of the Belgian mining engineer and geologist, Jean-Marie Graulich (1920-2015). It was officially recognized by the International Mineralogical Association (IMA) in 2002. It was first described based on material from the Oumlil-East prospect in the famous Bou Azzer district in Morocco, which is its type locality. ## Uses Due to its rarity and occurrence as microscopic crystals, graulichite-(Ce) has no industrial applications. It is of scientific and collecting interest only.

Properties

Mohs hardness: 4
Luster: Vitreous to Resinous
Streak: Pale yellow
Density: 4.35
Cleavage: None
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identifying graulichite-(Ce) based on visual characteristics is very difficult. Its occurrence as microscopic, yellow crystals in the oxidation zones of cobalt, nickel, and arsenic ore deposits is key. Co-occurrence with other arsenates, especially erythrite, is characteristic. ## Distinguishing from Similar Minerals The mineral is visually indistinguishable from other yellow arsenates and sulfates of the alunite supergroup, such as beudantite, segnitite, hidalgoite, or weilerite. Definitive differentiation requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS), to confirm the dominance of cerium and iron in its chemical composition. ## Crystal Forms It forms small, well-developed rhombohedral crystals, often modified in such a way that they resemble cubes (pseudocubic). It also occurs as crusts and earthy aggregates.

Geological environment

## Genesis Graulichite-(Ce) is a secondary mineral, formed in the oxidation zones (iron caps) of hydrothermal arsenide deposits rich in cobalt and and nickel. ## Mineral Associations It most commonly co-occurs with minerals such as erythrite, quartz, talc, dolomite, arsenopyrite, skutterudite, and loellingite. ## Localities The most important and type locality is the deposits in the Bou Azzer district in Morocco. It is also known from several other localities worldwide, including the Clara mine in the Black Forest, Germany.

Rarity

Very rare

For collectors

## Quality Criteria The quality of collector specimens, which are almost exclusively microminerals, is assessed based on the sharpness and development of the crystals, the intensity of their yellow color, and the aesthetics of the entire mineral assemblage on the rock matrix. Specimens with well-defined crystals contrasting with associated minerals, such as pink erythrite, are particularly prized. ## Popular Localities By far the most valued specimens, including the type material, come from the Bou Azzer district in Morocco. This is the main source of this mineral on the collector's market.

Care and storage

## Cleaning Specimens should be handled with extreme care due to their small size and fragility. For dust removal, it is best to use compressed air or a very soft brush. Contact with water should be limited; if necessary, use distilled water and immediately dry the specimen. ## What to Avoid As an arsenate, the mineral is toxic. Avoid inhaling dust and thoroughly wash hands after any contact. Do not expose it to strong acids, which can damage it. Keep away from children and pets. ## Storage The safest storage method is to place the specimen in a sealed “micromount” box, with an appropriate label containing the name and locality. This protects the fragile mineral from mechanical damage and accidental loss, and also limits contact with potentially toxic dust.

Sources

IMA Mineral List (CNMNC)