Magnesiocopiapite

Chemical formula: MgFe<sup>3+</sup><sub>4</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>6</sub>(OH)<sub>2</sub>·20H<sub>2</sub>O

Magnesiocopiapite is a hydrated magnesium and iron sulfate, forming characteristic yellow coatings and crusts in the oxidation zones of sulfide deposits.

## Characteristics Magnesiocopiapite is a secondary mineral belonging to the copiapite group. It typically occurs as small, tabular or scaly crystals forming granular aggregates, coatings, crusts, and efflorescences. Its crystals are very small, often microscopic in size, making them rarely visible to the naked eye. Specimens most often appear as powdery or earthy aggregates on the surface of other rocks. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2.5 to 3. It is light, with a density of approximately 2.13 g/cm³. Crystals exhibit a pearly luster, especially on cleavage surfaces, while earthy aggregates are dull. It is transparent to translucent. ## Colors and Varieties It is characterized by a light yellow, sulfur-yellow to yellowish-green color. No color or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1935 by George

Properties

Mohs hardness
2.5-3
Luster
Pearly
Streak
Light yellow
Density
2.13
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Magnesiocopiapite can be identified by its characteristic sulfur-yellow color, low hardness, and occurrence as earthy or powdery coatings and crusts. It often forms on rocks in dry, desert climates. Reaction with water (solubility) is a key diagnostic feature. ## Distinguishing from Similar Minerals It can be confused with other minerals from the copiapite group (e.g., copiapite), from which differentiation requires advanced chemical analyses (EDS, XRD). Jarosite can also have a similar appearance, but it is harder and does not dissolve in water. It differs from native sulfur by its form of occurrence (coatings, not distinct crystals) and formation environment. ## Crystal Forms It forms very small, tabular crystals, most often gathered in scaly, spherulitic, or earthy aggregates. Single, well-formed crystals are rarely observed.

Geological environment

## Genesis It is a secondary mineral, formed as a result of the weathering and oxidation of sulfide deposits, especially pyrite and chalcopyrite, in dry climates. It forms as a product of the evaporation of acidic mine waters and is a typical component of efflorescences in old mines and on mine dumps. ## Mineral Associations It co-occurs with other sulfates, such as copiapite, melanterite, gypsum, jarosite, epsomite, as well as with pyrite and goethite. ## Localities Significant occurrences of magnesiocopiapite are found in dry regions. It was discovered in Chuquicamata, Chile. It also occurs in the Island Mountain mine in California (USA), the Atacama Desert (Chile), Germany (Harz Mountains), and Utah (USA).

Rarity

Not very common

For collectors

## Quality Criteria Magnesiocopiapite specimens are primarily valued by collectors specializing in secondary, systematic, or locality-specific minerals. The most desirable samples are those with rich, intensely colored crusts covering a large surface area of the host rock. Due to the microscopic size of the crystals, their form is not the main evaluation criterion. ## Popular Localities The most classic and prized specimens come from the type locality in Chuquicamata, Chile, as well as from mines in California and Utah, USA, where it forms striking yellow coatings.

Care and storage

## Cleaning It should only be cleaned dry, using a soft brush to remove dust. Due to its water solubility, contact with liquids, including distilled water, should be avoided. ## What to Avoid The mineral is very sensitive to moisture and dissolves in water. It should be protected from all liquids, high humidity, and direct sunlight, which can cause fading and dehydration. It is unstable in contact with acids and bases. ## Storage Magnesiocopiapite specimens require storage in dry conditions, preferably in tightly sealed containers or display cases with a desiccant (e.g., silica gel). Avoid keeping it in humid rooms, such as basements.

Sources

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