Calciocopiapite
Chemical formula: CaFe<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
Calciocopiapite is a hydrated calcium and iron sulfate of the copiapite group, forming characteristic sulfur-yellow coatings and crusts.
Description
## Characteristics Calciocopiapite is a secondary mineral of the copiapite group, chemically classified as a hydrated calcium and iron sulfate. It most commonly occurs as earthy or powdery masses, as well as crusts and coatings. Less frequently, it forms small, well-formed tabular or platy crystals, aggregated into scaly masses. Its most characteristic feature is its intense, sulfur-yellow or lemon-yellow color. ## Physical Properties Calciocopiapite crystals are transparent to translucent and exhibit a pearly luster on cleavage planes, and a vitreous luster on other surfaces. Aggregates, however, are opaque and have a dull, earthy appearance. It is a relatively soft mineral, with a Mohs hardness of 2.5-3. Its density is low, approximately 2.1-2.2 g/cm³. ## Colors and Varieties This mineral ranges in color from sulfur-yellow, through lemon-yellow, to golden-yellow. No distinct color varieties or commercial names are recognized. ## History and Name The mineral's name, given in 1935 by Cornelius S. Hurlbut Jr. and Lester W. Strock, refers to its chemical composition (the presence of calcium - Latin *calx*) and its structural similarity to copiapite. It was first described based on samples from the Chuquicamata mine in Chile, which is its type locality. ## Uses Calciocopiapite has no industrial applications. However, it is an object of interest for mineral collectors and scientists studying the weathering processes of sulfide deposits.
Diagnostic features
## Identification Calciocopiapite can be identified by its characteristic sulfur-yellow color, low hardness, low density, and occurrence as coatings and crusts in the oxidation zones of sulfide deposits. Its presence is strongly associated with weathering pyrite and other iron sulfides. ## Distinguishing from Similar Minerals Macroscopic differentiation of calciocopiapite from other minerals of the copiapite group (e.g., copiapite) is practically impossible without chemical analysis confirming the presence of calcium. It can be confused with jarosite, which is, however, harder (2.5-3.5) and crystallizes in the trigonal system. Native sulfur is significantly lighter and softer (1.5-2.5). Other secondary iron sulfates, such as fibroferrite, are most often distinguished by their fibrous habit. ## Crystal Forms Crystals are rare, small, and in the form of thin tablets or plates. They usually form scaly, lamellar, or radial aggregates. Most often, however, calciocopiapite occurs in massive, earthy, or powdery aggregates and crusts.
Geological environment
## Genesis It is a typical secondary mineral, formed by the oxidation of pyrite or other iron sulfides in dry or semi-arid conditions. This process occurs in the weathering zones (gossans) of ore deposits, as well as on mine dumps and in old mine workings. The presence of calcium-rich solutions is essential for its formation. ## Mineral Associations Calciocopiapite often co-occurs with other secondary sulfates, such as copiapite, melanterite, gypsum, alunogen, fibroferrite, halotrichite, as well as with the primary mineral from which it forms - pyrite. ## Localities Important localities for this mineral worldwide include the Chuquicamata mine in Chile (type locality), deposits in Cyprus, the Rammelsberg mine in Germany, and numerous occurrences in Utah, USA (e.g., the Dexter mine).
Rarity
Not very common
Collector aspects
## Quality Criteria The most highly valued calciocopiapite specimens are characterized by an intense, pure, lemon-yellow color. The value of a specimen significantly increases if well-formed, even small, crystals are visible. Rich crusts on a contrasting rock matrix are also attractive. Due to the mineral's fragility and sensitivity, undamaged specimens with a large surface area are sought after by collectors. ## Popular Localities The type locality, Chuquicamata in Chile, is considered classic and provides the best specimens. High-quality collector material, often in the form of well-formed microcrystals, also comes from mines in Utah, USA.
Care and storage
## Cleaning The mineral is very sensitive to water, which can damage or completely dissolve it. Cleaning should only be done dry, using a soft brush to remove dust or a gentle stream of compressed air. Ultrasonic cleaners should be strictly avoided. ## What to Avoid Contact with water and other liquids must be strictly avoided. Calciocopiapite is a hydrated mineral, therefore it is sensitive to high temperatures, which can cause dehydration and subsequent disintegration. It should be protected from prolonged exposure to direct sunlight and stored away from heat sources. High humidity is also harmful. ## Storage Calciocopiapite specimens are best stored in a dry and stable environment. Sealed, airtight containers or display cases with a desiccant (e.g., silica gel) are recommended to protect the mineral from changes in ambient humidity.