Magnesiobeltrandoite-2N3S

Chemical formula: (Mg₆Al₂)(Al₁₈Fe₃+₂)O₃₈(OH)₂

An extremely rare mineral from the högbomite supergroup, forming microscopic, black, hexagonal crystals.

## Characteristics Magnesiobeltrandoite-2N3S is a very rare oxide from the högbomite supergroup, defined as a distinct mineral species in 2021. It occurs as small, subhedral to euhedral (partially or fully developed) crystals with a hexagonal prismatic habit. Its size is microscopic, usually not exceeding 0.15 mm. Specimens are black and have a metallic luster. ## Physical Properties The mineral is opaque. Hardness on the Mohs scale has not been precisely measured, but for minerals in this group, it is estimated to be 6.5-7. The density calculated from the formula and unit cell parameters is 3.84 g/cm³. No cleavage has been observed. ## Colors and Varieties Magnesiobeltrandoite-2N3S occurs exclusively in black. No color or commercial varieties are known. ## History and Name The mineral's name reflects its chemical composition and structure. The "Magnesio-" prefix indicates magnesium as the dominant divalent cation. "Beltrandoite" refers to its relationship with the mineral beltrandoite-2N2S. The suffix "-2N3S" is a technical designation describing the sequence and proportions of alternating nolanite (N) and spinel (S) modules in the crystal structure. The mineral was officially approved by the IMA under number 2021-085, and its discovery was described based on specimens from the Cava del Brutto quarry in Italy. ## Applications Due to its extreme rarity and microscopic size, magnesiobeltrandoite-2N3S has no commercial or industrial applications. It is solely an object of scientific research and interest for specialized micromineral collectors.

Properties

Luster: Metallic
Streak: Brown-black
Density: 3.84
Cleavage: None
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of magnesiobeltrandoite-2N3S is impossible based on visual characteristics alone. Its black color, metallic luster, and hexagonal crystal shape are common to many other minerals. Definitive identification requires advanced analytical techniques, such as X-ray diffraction (XRD) to determine the crystal structure and chemical analysis (EDS/WDS) to confirm the composition. ## Differentiation from Similar Minerals The mineral is visually indistinguishable from other black, metallic minerals of the högbomite supergroup, such as beltrandoite-2N2S, magnesiohögbomite-2N2S, or nolanite. It can also be confused with small crystals of spinel (hercynite), hematite, or ilmenite, which may occur in the same environment. Differences can only be determined by laboratory methods. ## Crystal Forms It forms short, hexagonal prismatic crystals, often with incompletely developed faces (subhedral).

Geological environment

## Genesis Magnesiobeltrandoite-2N3S forms under conditions of high-temperature metamorphism or metasomatism. At its type locality, it was found in phlogopite-rich veins cutting calcitic-dolomitic marbles. These marbles occur as xenoliths (fragments of foreign rocks) within a peridotite massif. ## Mineral Associations It co-occurs with a rich assemblage of minerals, including phlogopite, calcite, dolomite, forsterite, clinochlore, spinel, geikielite, hematite, and other rare minerals from the högbomite supergroup. ## Localities The only confirmed locality for this mineral in the world is its type locality – the Cava del Brutto quarry in Premosello-Chiovenda, in the province of Verbano-Cusio-Ossola, Piedmont, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of specimens of this micromineral is assessed based on several criteria. The most important is the confirmation of the mineral's identity through analysis. Collectors value specimens with well-formed, sharp (euhedral) crystals, even if they are microscopic. Contrast with the surrounding rock matrix and the presence of interesting associated minerals are also important. ## Popular Localities Since the mineral is known from only one location in the world, all available specimens come from the Cava del Brutto quarry in Italy. This is therefore the only and most prized locality.

Care and storage

## Cleaning Specimens are microscopic and usually housed in special micromount boxes. Cleaning, if absolutely necessary, should be limited to gently removing dust with a photographic air blower or a soft brush. Avoid contact with water and any chemicals. ## What to Avoid The mineral is stable, but ultrasonic cleaners should be avoided, as they could damage or detach tiny crystals from the matrix. Contact with acids and other aggressive chemicals should also be avoided. ## Storage The safest form of storage is a specialized micromount box, which protects the delicate specimen from dust, shocks, and mechanical damage. It does not require special conditions regarding temperature or humidity.

Sources

IMA Mineral List (CNMNC)

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