Millosevichite

Chemical formula: Al<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>3</sub>

Millosevichite is a rare aluminum sulfate, occurring as fine coatings and aggregates, mainly associated with volcanic activity.

## Characteristics Millosevichite is a rare, anhydrous aluminum sulfate. It typically forms very fine, earthy or powdery coatings and crusts on rocks. Due to the small size of its crystals, its macroscopic features are difficult to observe. It occurs as aggregates of microscopic, hexagonal crystals or as coatings on lava and in fumaroles. ## Physical Properties This mineral is characterized by a vitreous luster. It is transparent to translucent. Due to its mode of occurrence, determining its hardness and density is problematic, and these data are not precisely established. ## Colors and Varieties Millosevichite is usually white, sometimes with a yellowish or reddish tint, which may be caused by the presence of impurities, e.g., iron compounds. No named varieties are distinguished. ## History and Name The mineral was first described in 1913 by Guido Pelloux. The name commemorates Federico Millosevich (1875-1942), an Italian mineralogist from the University of Rome. The type locality is Grotta dell'Allume on Vulcano Island (Aeolian Islands) in Italy. ## Uses Millosevichite has no industrial application. It is solely an object of scientific interest and a collector's item for specialized collectors of rare minerals.

Properties

Luster
Vitreous
Streak
White
Cleavage
None
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Identifying millosevichite under amateur conditions is practically impossible. Identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). In the field, it can be suspected in specific environments – as white or yellowish coatings in active volcanic fumaroles. ## Distinguishing from Similar Minerals It can be confused with many other sulfates and volcanic exhalation products, such as alunite, alunogen, gypsum, or thenardite. Differentiation without specialized equipment is not possible. The key is its association with aluminum and the absence of water in its structure, which can only be confirmed in the laboratory. ## Crystal Forms It forms microscopic, tabular crystals with a hexagonal outline. Most often, it occurs as very fine-grained, powdery or earthy aggregates, coatings, and thin crusts.

Geological environment

## Genesis Millosevichite is a mineral of volcanic origin. It forms as a result of fumarolic activity, where hot volcanic gases rich in sulfur oxides react with aluminum-containing rocks. It crystallizes at high temperatures, often above 200°C. It is also found as a product of burning mine dumps. ## Mineral Associations It co-occurs with other fumarolic and oxidation zone minerals, such as salammoniac, native sulfur, hematite, and other rare sulfates. ## Localities Key localities worldwide include the type locality on Vulcano Island in Italy, Mutnovsky volcano in Kamchatka (Russia), Tolbachik volcanic complex (Russia), as well as burning coal dumps in Pennsylvania (USA) and Kopeysk (Russia).

Rarity

Very rare

For collectors

## Quality Criteria In the case of millosevichite, collectible value does not depend on aesthetics, which are minimal. The most important criteria are the richness and abundance of the coating on the host rock and precise confirmation of the mineral's identification. Specimens from a well-documented, classic locality (like Vulcano) are more valued. Due to its microscopic nature, specimens do not reach large sizes. ## Popular Localities The most sought-after specimens by collectors specializing in rare minerals are those from the type locality – Grotta dell'Allume on Vulcano Island. Samples from active volcanoes, such as Tolbachik in Kamchatka, are also valuable.

Care and storage

## Cleaning Millosevichite specimens are extremely delicate and often water-soluble. They should absolutely not be cleaned wet. The safest method is to remove dust with a soft brush or a photographic air blower, exercising the utmost caution. ## What to Avoid Avoid contact with water and any chemicals that could dissolve or damage it. The mineral is sensitive to moisture, so it should be protected from high humidity. Shocks and abrasion should also be avoided due to its fragility and mode of occurrence. ## Storage Specimens should be stored in a dry place, preferably in a sealed, airtight box (such as a "membrane box" or a box with a desiccant). Exposure should be away from sources of moisture and direct sunlight, at a stable temperature.

External references

Sources

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