Paracoquimbite

Chemical formula: Fe<sup>3+</sup><sub>4</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>6</sub>(H<sub>2</sub>O)<sub>12</sub>·6H<sub>2</sub>O

Paracoquimbite is a rare, secondary iron sulfate, forming small, purple crystals, often in association with other sulfates.

## Characteristics Paracoquimbite is a hydrated iron sulfate, occurring as small, well-formed crystals. It usually forms granular aggregates or crusts. Its crystals have the form of hexagonal tablets or short prisms, reaching sizes up to several millimeters. It is a secondary mineral, formed in the oxidation zones of ore deposits, often in dry and hot climates. ## Physical Properties Paracoquimbite crystals are characterized by a vitreous luster. The mineral is brittle, and its Mohs hardness is approximately 2.5. The density is low, approximately 2.11 g/cm³. It is transparent to translucent. Due to its water solubility, it is unstable in humid environments. ## Colors and Varieties Paracoquimbite most often ranges in color from pale lilac and light purple to almost colorless. No color or commercial varieties are distinguished. ## History and Name The mineral was first described in 1933 by Joseph Murgoci. Its name refers to its structural and chemical similarity to coquimbite, with the prefix "para-", which in crystallography denotes a polymorphic variety with different symmetry. It was discovered in the Alcaparrosa mine in the province of El Loa, Chile. ## Uses Paracoquimbite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals or secondary minerals.

Properties

Mohs hardness
2.5
Luster
Vitreous
Streak
White
Density
2.11
Cleavage
None
Fracture
Conchoidal
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Paracoquimbite is identified by its characteristic purple color, trigonal crystal habit (hexagonal tablets), and occurrence in paragenesis with other secondary sulfates. A key feature is its water solubility. ## Distinguishing from Similar Minerals It can be confused with coquimbite, which has a very similar composition and appearance. Differentiation requires advanced methods, such as X-ray diffraction (XRD), as they differ in crystallographic system (coquimbite is trigonal, paracoquimbite also, but they belong to different space groups). It is distinguished from amethyst (quartz) by its extremely low hardness. ## Crystal Forms Crystals are typically tabular, with a hexagonal outline, or short prismatic. It occurs as single, small crystals or in granular and powdery aggregates.

Geological environment

## Genesis It is a secondary mineral, formed by the oxidation of sulfide minerals (mainly pyrite) in dry and desert conditions. It forms as a product of evaporation of acidic mine waters or as a product of volcanic exhalations (fumaroles). ## Mineral Associations It often co-occurs with other iron sulfates, such as coquimbite, kornelite, romerite, voltaite, as well as with pyrite, marcasite, and native sulfur. ## Localities The most important localities worldwide include the Alcaparrosa mine in the Antofagasta region, Chile (type locality), the Iron Knob iron deposit in South Australia, the Dexter No. 7 mine in Emery County, Utah (USA), and the La Fossa volcanic complex on Vulcano Island, Italy.

Rarity

Rare

For collectors

## Quality Criteria The most prized paracoquimbite specimens are those with well-formed, sharp crystals of intense, purple color. Association with other rare sulfates, creating aesthetic contrasts, is also important. Due to the small size of the crystals, micromount specimens are standard. ## Popular Localities The best localities for this mineral are considered to be those in Chile, especially the Alcaparrosa mine, from which classic specimens originate. Crystals from fumaroles on Vulcano Island, Italy, are also highly valued.

Care and storage

## Cleaning Paracoquimbite specimens should not be wet cleaned, as the mineral is water-soluble. Dust can be removed very carefully using a soft brush or a stream of compressed air from a safe distance. ## What to Avoid Contact with water, water vapor, and high air humidity must be strictly avoided, as these can cause dissolution or chemical degradation of the mineral. It should also be protected from chemicals and sudden temperature changes. ## Storage Paracoquimbite requires storage in dry conditions. It is best to place it in an airtight, sealed box (such as a "membrane box" or with a desiccant), away from sources of moisture and direct sunlight.

Sources

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