Malladrite

Chemical formula: Na₂SiF₆

Malladrite is a rare sodium fluorosilicate, occurring as small, hexagonal crystals in volcanic exhalations.

## Characteristics Malladrite is a rare mineral from the fluorosilicate group; chemically, it is sodium fluorosilicate. It typically forms very small, hexagonal crystals with a platy or prismatic habit. It occurs as coatings, crusts, and granular aggregates on volcanic rocks, often in association with other fumarolic minerals. Due to the small size of its crystals, its visual features are difficult to observe with the naked eye. ## Physical Properties This mineral is characterized by low hardness, measuring 3 on the Mohs scale. It is relatively light, with a density of approximately 2.71 g/cm³. The crystals are translucent and exhibit a vitreous luster. ## Colors and Varieties Malladrite is most commonly colorless or white. Specimens with a delicate, pale pink hue are also found. No distinct color or commercial varieties are recognized. ## History and Name The mineral was first described in 1926. Its name comes from Alessandro Malladra (1865-1945), an Italian volcanologist and director of the Vesuvius Observatory, who made significant contributions to the study of volcanic activity. The type locality of discovery is Mount Vesuvius in Italy.

Properties

Mohs hardness
3
Luster
Vitreous
Density
2.714
Cleavage
{0001}
Transparency
Translucent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of malladrite is based on its occurrence environment – it is a product of volcanic exhalations. Characteristic features include small, hexagonal crystals forming coatings. A key characteristic is its water solubility, which distinguishes it from many other minerals. It reacts with sulfuric acid, releasing hydrogen fluoride. ## Distinguishing from Similar Minerals It can be confused with other white or colorless fumarolic minerals, such as sal ammoniac or hieratite. Differentiation in the field is practically impossible and requires chemical analysis (EDS/XRD). A water solubility test can be a helpful indicator. ## Crystal Forms It forms small, platy or short-prismatic crystals with a hexagonal outline. It occurs mainly as fine-grained aggregates, coatings, and crusts.

Geological environment

## Genesis Malladrite is a mineral of volcanic origin. It forms through sublimation from volcanic gases (exhalations) in fumaroles, where hot gases rich in fluorine and silicon compounds react with sodium present in the environment. It crystallizes at temperatures ranging from 100 to 250°C. ## Mineral Associations It co-occurs with other minerals formed under similar conditions, such as hieratite, sylvite, halite, and native sulfur. ## Localities The most important and type locality for malladrite is the volcanic complex of Mount Vesuvius and the nearby Phlegraean Fields in Campania, Italy. It has also been reported in exhalations from Mount Etna in Sicily and Mutnovsky Volcano in Kamchatka, Russia.

Rarity

Rare

For collectors

## Quality Criteria The quality of a malladrite specimen primarily depends on the richness of the coating and the degree of development of visible crystals, which is rare. Since crystals are usually microscopic, specimens with visible, even small, hexagonal crystals are most desirable. Aesthetic composition with the rock matrix is also important. ## Popular Localities The vast majority of collector specimens, including those of the highest quality, come from historical and contemporary exhalations of Mount Vesuvius in Italy.

Care and storage

## Cleaning Due to its water solubility, malladrite should not be cleaned with water. Only gentle mechanical dust removal using a soft brush or compressed air from a safe distance is permissible. ## What to Avoid Contact with water and other liquids, which can dissolve or damage the mineral, must be absolutely avoided. It is sensitive to high humidity, which can lead to its gradual degradation. It should be protected from chemicals and ultrasound. ## Storage Malladrite specimens require storage in dry conditions. The best solution is to place them in a sealed container (e.g., a "perky box") with a desiccant (e.g., silica gel).

External references

Sources

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