Magnesioaubertite

Chemical formula: MgAl(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>Cl·14H<sub>2</sub>O

Magnesioaubertite is a very rare, water-soluble sulfate, forming blue, acicular crystals and efflorescences.

## Characteristics Magnesioaubertite is a hydrated magnesium and aluminum sulfate with added chlorine. It occurs as very small, acicular or hair-like crystals, which often form aggregates, efflorescences, and crusts. Due to its delicate nature and small crystal size, individual forms are usually visible only under magnification. ## Physical Properties Magnesioaubertite crystals are very soft and brittle. This mineral is completely soluble in water. It has a vitreous luster. ## Colors and Varieties It is characterized by a pale blue to blue color. No varieties have been distinguished. ## History and Name The mineral's name refers to its chemical composition – the dominance of magnesium (magnesio) – and its structural relationship to aubertite. It was recognized as a new mineral by the International Mineralogical Association (IMA) in 1993. It was described by J. J. Martínez-Frías and co-workers. ## Uses Magnesioaubertite has no industrial applications. It is solely of interest to collectors specializing in rare minerals and to scientists.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
White
Density
1.84
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Transparent
Crystal system
Triclinic

Diagnostic features

## Identification A key diagnostic feature is its water solubility. Its characteristic blue color, acicular crystal habit, and occurrence as efflorescences and crusts in a specific environment (volcanic fumaroles) are also distinctive. ## Distinguishing from Similar Minerals It can be confused with other secondary sulfates of similar color and form, such as chalcanthite or aubertite. Differentiation requires chemical analysis (EDS/XRD); however, chalcanthite is associated with copper deposits, and aubertite contains copper instead of magnesium. Water solubility distinguishes it from most blue minerals. ## Crystal Forms It forms very fine, acicular or hair-like crystals, elongated along the [001] axis. These crystals aggregate as efflorescences, crusts, bundles, and fibrous masses.

Geological environment

## Genesis Magnesioaubertite is a secondary mineral, formed by the activity of volcanic fumaroles. It crystallizes directly from volcanic gases in lower temperature zones through a resublimation process. ## Mineral Associations It co-occurs with other fumarolic minerals, such as aubertite, eriostrakonit, metavoltine, native sulfur, as well as chlorides (halite, sylvite) and alums. ## Localities The type and main locality for this mineral are the fumaroles of the Vesuvius volcano in Italy. It has also been identified in the Alcaparrosa mine in San Juan Province, Argentina.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a specimen primarily depends on the intensity and saturation of the blue color and on the abundance and coverage of the host rock surface by magnesioaubertite efflorescences. Since the crystals are microscopic, their individual form is not the main evaluation criterion. Rich, well-colored, and stable specimens on an aesthetic rock matrix are valued. ## Popular Localities The most known and valued specimens come from the Vesuvius-Somma volcanic complex in Italy, which is its type locality.

Care and storage

## Cleaning The mineral **must not be cleaned wet**, as it is completely soluble in water. Specimens should only be cleaned using a soft brush or compressed air to remove dust. ## What to Avoid Contact with water and all liquids must be strictly avoided. The mineral is hygroscopic, so it must be protected from humid air, which can cause its disintegration. Avoid temperature changes and direct sunlight. ## Storage Magnesioaubertite specimens must be stored in sealed, airtight containers (e.g., "perky box" type) away from moisture. It is advisable to place a desiccant (silica gel) nearby. Store at a stable room temperature.

Sources

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