Magnesiohögbomite-6N12S

Chemical formula: Mg₅Al₁₁Ti₄+O₂₃(OH)

Magnesium, aluminum, and titanium oxide from the högbomite group, forming microscopic, hexagonal crystals of dark brown or black color.

## Characteristics Magnesiohögbomite-6N12S is a very rare mineral belonging to the högbomite supergroup. It occurs as very small, tabular or short-prismatic crystals with a hexagonal outline, rarely exceeding 0.5 mm in size. It is usually intergrown with other minerals. It is dark brown to black in color and is opaque or at most translucent on thin edges. ## Physical Properties This mineral is characterized by a hardness of 6.5 on the Mohs scale, making it relatively scratch-resistant. It has a vitreous luster and a conchoidal fracture. It does not exhibit cleavage. Its density, calculated based on the formula and cell parameters, is approximately 3.78 g/cm³. ## Colors and Varieties The observed colors are exclusively dark brown and black. No color varieties or trade names are known for this mineral. ## History and Name The mineral's name indicates its chemical composition (dominant magnesium - "magnesio") and its belonging to the högbomite group. The "-6N12S" component is a structural descriptor, describing the stacking sequence of nolanite-type (N) and spinel-type (S) layers in its crystal structure (six nolanite layers to twelve spinel layers). It was approved as a new mineral species in 2002. ## Applications Due to its extreme rarity and microscopic size, magnesiohögbomite-6N12S has no industrial applications. It is solely an object of scientific research and is valued by specialized collectors of rare minerals (so-called micromounts).

Properties

Mohs hardness: 6.5
Luster: Vitreous
Streak: Grey
Density: 3.78
Cleavage: None
Fracture: Conchoidal
Transparency: Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Visual identification is practically impossible and unreliable. Recognition requires advanced analytical techniques, such as chemical analysis by electron microprobe (EDS/WDS) and X-ray diffraction (XRD) to confirm its unique polytypic structure. An indicative feature may be the hexagonal habit of the crystals and co-occurrence with specific minerals in high-grade metamorphic rocks. ## Distinguishing from Similar Minerals It can be confused with other dark, hard minerals found in similar environments, such as spinel, ilmenite, magnetite, and especially with other minerals from the högbomite supergroup (e.g., magnesiohögbomite-2N4S or nolanite). Definitive differentiation is only possible based on detailed laboratory analyses. ## Crystal Forms It forms small, tabular or prismatic crystals with a hexagonal cross-section. They usually occur as single grains intergrown with other minerals.

Geological environment

## Genesis This is a mineral typical of rocks that have undergone metamorphism under granulite facies conditions, i.e., at very high temperatures and pressures. Its formation is associated with metasomatism and desilication processes (removal of silica) within ultramafic rocks. ## Mineral Associations It most commonly co-occurs with corundum (both as inclusions within it and alongside it), spinel, gedrite, plagioclase, sapphirine, staurolite, kyanite, and biotite. ## Localities The only confirmed locality for this specific polytype (type locality) is the Subotsy ultramafic massif in the Kirovohrad Oblast, Ukraine.

Rarity

Extremely rare

For collectors

## Quality Criteria For micromount minerals, the main criterion of value is the quality of the crystal itself – its sharpness, well-formed faces, and lack of damage. Its size (even if sub-millimeter) and the visual attractiveness of the matrix and associated minerals are also important. The certainty of the specimen's identification, confirmed by a reliable analyst or institution, is crucial. ## Popular Localities The only source of specimens is the type locality in Ukraine. Specimens from this location are extremely difficult to obtain.

Care and storage

## Cleaning Specimens of this mineral are typically micromounts that rarely require cleaning. If necessary, compressed air can be used to remove dust or a very soft, dry brush. Avoid wet cleaning and the use of any chemical agents. ## What to Avoid The mineral is stable, but it should be protected from mechanical damage, shocks, and abrasion, which could damage the delicate crystals. Avoid contact with acids. ## Storage The safest storage method is to place the specimen in a specialized micromount box. This protects the mineral from dust, moisture, and mechanical damage, while allowing for observation under a microscope.

Sources

IMA Mineral List (CNMNC)

Magnesiohögbomite-6<i>N</i>12<i>S</i>