Magnanelliite

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

Magnanelliite is an extremely rare potassium iron sulfate, forming microscopic, tabular, yellowish-brown crystals in volcanic exhalations.

## Characteristics Magnanelliite is a hydrated potassium iron sulfate belonging to the metavoltine group. It occurs as very small, thin, tabular crystals with a hexagonal outline, rarely exceeding 0.2 mm in diameter. These crystals most often form rosette-like aggregates, fan-shaped aggregates, or thin crusts on the substrate. The mineral is characterized by a vitreous luster and is transparent to translucent. ## Physical Properties Due to the microscopic size of the crystals, many physical properties have not been fully investigated. Hardness is not determined, but like other sulfates in this group, it is a very brittle and delicate mineral. The calculated density is 2.80 g/cm³. It exhibits perfect cleavage in one plane. ## Colors and Varieties Magnanelliite occurs in shades from yellowish-brown to reddish-brown. Its streak is light yellow. No varieties of this mineral have been distinguished. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2013. Its name honors Dr. Stefano Magnanelli (born 1959), an Italian chemist and amateur collector who discovered this mineral. The type locality is the La Fossa crater on Vulcano Island (Aeolian Islands), Italy. ## Uses Magnanelliite has no industrial application. It is of interest only for scientific study and for specialized collectors of microscopic minerals (so-called micromounts).

Properties

Luster
Vitreous
Streak
Pale yellow
Density
2.80
Cleavage
Perfect on {0001}
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Amateur identification of magnanelliite is impossible. Due to the microscopic size of the crystals and its occurrence in complex parageneses, it requires advanced analytical techniques such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). Preliminary indications may include the tabular habit of the crystals, yellowish-brown color, and specific occurrence environment (volcanic fumaroles). ## Distinguishing from Similar Minerals Magnanelliite can be confused with many other sulfates formed in fumarolic environments, such as metavoltine, krausite, or jarosite. All these minerals form similar yellow or brown crusts and aggregates. Definitive distinction is only possible based on laboratory analysis. ## Crystal Forms The mineral forms thin, tabular crystals with a hexagonal outline. These crystals most often occur as fan-shaped or rosette-like aggregates and fine-grained crusts.

Geological environment

## Genesis Magnanelliite is a volcanic mineral, crystallizing directly from gases (sublimates) in high-temperature fumaroles. It forms at a temperature of approximately 300°C in an environment rich in sulfur, potassium, and iron. ## Mineral Associations At the type locality (La Fossa crater), magnanelliite coexists with other fumarolic minerals such as adranosite, alunogen, anhydrite, bismuthinite, sassolite, and sal ammoniac. ## Localities The only confirmed locality for magnanelliite in the world is its type locality – an active fumarole in the La Fossa crater on Vulcano Island, part of the Aeolian Islands archipelago in Sicily, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the collector's value of a specimen depends on several factors. Samples with well-formed, sharp crystals forming aesthetic, rosette-like aggregates are most highly prized. The intensity and purity of the color, as well as the abundance of occurrence on the rock matrix, are also important. The presence of other rare associated minerals on the same specimen increases its attractiveness. ## Popular Localities The only source of magnanelliite specimens is the La Fossa crater on Vulcano Island, Italy. Material from this locality is extremely rare and sought after by specialized collectors.

Care and storage

## Cleaning Magnanelliite specimens are extremely delicate and sensitive. The only safe method for dust removal is very careful use of compressed air from a safe distance or a soft, dry brush. Absolutely avoid contact with water and all liquids. ## What to Avoid The mineral is likely soluble in water or at least negatively affected by it. It should be protected from moisture, temperature changes, and all chemicals. Due to its brittleness, it is very susceptible to mechanical damage. ## Storage It is recommended to store specimens only in tightly sealed micromount boxes, which protect against dust, moisture, and physical damage. Avoid exposure to direct sunlight and humidity fluctuations.

Sources

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