Magnesiohögbomite-2<i>N</i>2<i>S</i>

Chemical formula: (Al,Mg,Fe<sup>2+</sup>,Fe<sup>3+</sup>,Ti<sup>4+</sup>)<sub>22</sub>(O,OH)<sub>32</sub>

Magnesiohögbomite-2N2S is a rare magnesium, aluminum, and iron oxide, forming small, hexagonal crystals with a dark color and vitreous luster.

## Characteristics Magnesiohögbomite-2N2S is a complex oxide belonging to the högbomite group. It typically forms small, tabular or prismatic crystals with a hexagonal outline, rarely exceeding a few millimeters in size. It occurs as grains embedded in rock, which can be partially or completely transparent. Its name reflects the dominance of magnesium in its chemical composition and its specific crystal structure (2N2S polytype). ## Physical Properties This mineral is characterized by significant hardness, ranging from 6.5 to 7 on the Mohs scale, making it scratch-resistant. It has a vitreous, and on some surfaces, almost metallic luster. It is a relatively dense mineral, and its crystals are brittle. ## Colors and Varieties The typical coloration of magnesiohögbomite-2N2S is dark brown to almost black. In thin fragments or under strong light, it can be translucent, revealing reddish-brown or brown hues. No named varieties are distinguished. ## History and Name The mineral's name comes from its chemical composition with dominant magnesium (Magnesio-), a reference to the högbomite group, and its crystal structure (2N2S polytype). The group was named in honor of Arvid Gustaf Högbom (1857–1940), a Swedish geologist and professor at Uppsala University. Magnesiohögbomite-2N2S was formally described as a distinct mineral species in later years as part of a revision of the entire högbomite supergroup. ## Uses Due to its rarity and small crystal size, magnesiohögbomite-2N2S has no industrial applications. It is of purely scientific and collector's interest.

Properties

Mohs hardness
6.5 - 7
Luster
Vitreous to submetallic
Streak
Brown
Density
3.79 - 3.85
Cleavage
Imperfect on {0001}
Fracture
Conchoidal to uneven
Transparency
Transparent to translucent in thin fragments
Crystal system
Hexagonal

Diagnostic features

## Identification Amateur identification of magnesiohögbomite-2N2S is practically impossible. It requires advanced analytical methods, such as chemical analysis (EDS) and X-ray diffraction (XRD) to confirm composition and structure. Preliminary identification is based on the hexagonal crystal form, dark color, high hardness, and specific occurrence environment (metamorphic rocks). ## Distinguishing from Similar Minerals Magnesiohögbomite-2N2S can be confused with other minerals from the högbomite group, as well as tourmaline (especially schorl), spinel (hercynite, pleonaste), or ilmenite. Differentiation from other högbomite polytypes is only possible by laboratory methods. It differs from tourmaline by the absence of striations on prism faces, and from spinel and ilmenite by a slightly different crystal form and luster. ## Crystal Forms Crystals are typically tabular, with a hexagonal outline, less commonly short-prismatic. They occur as single grains embedded in rock or small, imperfect crystals.

Geological environment

## Genesis Magnesiohögbomite-2N2S is a mineral of metamorphic rocks that have undergone transformation under high temperatures and pressures, particularly in the amphibolite and granulite facies. It forms in rocks rich in aluminum and magnesium, and poor in silica, such as some gneisses, amphibolites, or calcite-dolomite marbles with an admixture of corundum and spinel. ## Mineral Associations It most commonly co-occurs with corundum, spinel (pleonaste), hercynite, phlogopite, pargasite, chondrodite, clinohumite, calcite, and dolomite. The presence of these minerals is an important diagnostic indicator. ## Localities Key confirmed localities worldwide include: the Cortlandt area in New York State (USA), where it occurs in emery deposits (corundum-magnetite rocks); the Tallgruvan deposit in the Norberg area, Sweden; the Zhdanov deposit in the Kovdor massif on the Kola Peninsula, Russia; as well as occurrences in Tanzania and Sri Lanka.

Rarity

Very rare

For collectors

## Quality Criteria Specimens with well-formed, sharp crystals with a distinct hexagonal outline are most valued by collectors. Contrast with a light host rock (e.g., marble) and the presence of associated minerals such as spinel or corundum are also important. Crystal size is a key factor – any specimen with crystals exceeding a few millimeters is considered exceptional. ## Popular Localities Localities in the USA (Cortlandt, New York) and Sweden (Tallgruvan) are considered classic and provide the best specimens. Specimens from these locations are historically important and serve as a reference point for this mineral.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush or paintbrush to remove dust. For heavier soiling, compressed air can be used. Due to the possible presence of sensitive associated minerals, water and chemical agents should be avoided. ## What to Avoid Avoid contact with acids and other chemicals that may damage the mineral's surface or the host rock. The mineral is hard but brittle, so it should be protected from impacts and falls. It does not require special protection from light or temperature. ## Storage It is best to store specimens in closed display boxes to protect them from dust and mechanical damage. A label with the locality is crucial for scientific and collector value.

Sources

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