Ferricopiapite

Chemical formula: Fe³⁺₂/₃Fe³⁺₄(S⁶⁺O₄)₆(OH)₂·₂₀H₂O

Ferricopiapite is a hydrated iron sulfate from the copiapite group, forming characteristic yellow coatings and crusts in the oxidation zones of sulfide deposits.

## Characteristics Ferricopiapite is a secondary mineral belonging to the copiapite group. It forms as a result of the weathering of sulfide minerals, mainly pyrite. It most often occurs as fine-grained, earthy, or powdery aggregates, as well as crusts and coatings. Less frequently, it forms small, tabular crystals gathered in rosette-like aggregates. It is a brittle mineral. ## Physical Properties Ferricopiapite is characterized by low hardness, ranging from 2.5-3 on the Mohs scale, which means it can be scratched with a fingernail. Its density is low, approximately 2.14 g/cm³. This mineral exhibits perfect cleavage in one direction. The luster is usually pearly, especially visible on cleavage surfaces, or dull in the case of earthy aggregates. ## Colors and Varieties This mineral takes on colors from light yellow to yellowish-orange. Its color is very characteristic and often allows for preliminary identification in the field. There are no named color varieties or commercial varieties. ## History and Name The name "ferricopiapite" refers to its chemical composition – a high content of trivalent iron (Latin: *ferrum* – iron) and its connection to copiapite, the main mineral in the group. It was described as a distinct mineral species in 1938. The type locality (first discovery) is in the Atacama region of Chile, near the town of Copiapó, which gave its name to the entire group of minerals. ## Uses Ferricopiapite has no industrial significance. However, it is of interest to collectors specializing in secondary minerals, mineralogical systematics, and minerals from specific localities.

Properties

Mohs hardness: 2.5-3
Luster: Pearly
Streak: Yellow
Density: 2.14
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Translucent
Crystal system: Triclinic

Diagnostic features

## Identification Ferricopiapite is most easily recognized by its characteristic, intensely yellow color, low hardness (can be scratched with a fingernail), and typical occurrence as coatings and crusts on other minerals, especially sulfides. The pearly luster on cleavage surfaces is also a helpful feature. ## Distinguishing from similar minerals This mineral can be confused with other yellow secondary sulfates, such as jarosite or other minerals from the copiapite group. Jarosite is usually harder and has a more vitreous or earthy luster. Final distinction from other members of the copiapite group often requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal forms Ferricopiapite crystals are rare and usually very small, with a tabular habit. Most often, they form rosette-like or scaly aggregates. However, the dominant form of occurrence is microcrystalline, powdery, or earthy coatings and massive crusts.

Geological environment

## Genesis Ferricopiapite is a typical secondary mineral. It forms in the oxidation zones (so-called iron caps) of ore deposits rich in sulfides, primarily pyrite (FeS₂). It forms under strongly acidic conditions, as a result of the weathering and decomposition of primary sulfide minerals under the influence of water and atmospheric oxygen. ## Mineral associations This mineral often co-occurs with other secondary iron sulfates. Its most common associates are other minerals from the copiapite group, as well as melanterite, jarosite, voltaite, halotrichite, and gypsum. It often grows directly on weathering pyrite or marcasite. ## Localities The most important occurrences of ferricopiapite are found in dry, desert climates, which favor the preservation of hydrated sulfates. Classic specimens come from the Atacama region in Chile (type locality). Other known localities include Island Mountain mine in California (USA), Rammelsberg in the Harz Mountains (Germany), and mine dumps in Spain (e.g., Rio Tinto).

Rarity

Not very common

For collectors

## Quality criteria Specimens with well-formed, even if small, crystals forming aesthetic aggregates are most valued by collectors. An intense, clean, yellow color is important. The attractiveness is also enhanced by the contrasting placement of ferricopiapite on dark matrix rock or in association with other well-defined accessory minerals. Due to its brittleness, specimens undamaged during collection are rated much higher. ## Popular localities Specimens from the type locality in Chile and from classic European localities, such as the Rammelsberg mine in Germany, are sought after by collectors specializing in systematics or mining history. Good quality microcrystals also come from some mines in California, USA.

Care and storage

## Cleaning Ferricopiapite specimens are very delicate and sensitive to water. Cleaning should be limited to an absolute minimum. Only gentle dust removal with a soft brush or a stream of compressed air from a safe distance is permissible. Any contact with water, which can dissolve or damage the mineral, should be avoided. ## What to avoid Contact with water, water vapor, and all chemicals, including acids and detergents, must be strictly avoided. Ferricopiapite is an unstable mineral under high humidity conditions – it can absorb or lose water from the air, leading to its disintegration. It should be protected from high temperatures and direct sunlight. ## Storage It is recommended to store specimens in a dry place, preferably in tightly sealed containers (e.g., "membrane box" type) or in boxes with a desiccant (silica gel). Display should be in closed display cases, away from sources of moisture and sudden temperature changes.

External references

https://www.mindat.org/min-1490.html