Magnesiohögbomite-6<i>N</i>6<i>S</i>

Chemical formula: (Mg,Al,Fe<sup>2+</sup>,Fe<sup>3+</sup>)<sub>3</sub>(Al,Ti<sup>4+</sup>)<sub>8</sub>O<sub>15</sub>(OH)

Magnesiohogbomite-6N6S is a very rare oxide of magnesium, aluminum, and iron, occurring as microscopic, hexagonal crystals in metamorphic rocks.

## Characteristics Magnesiohogbomite-6N6S is a complex oxide belonging to the hogbomite group. It forms very small, most often microscopic, tabular or prismatic crystals with a hexagonal outline. It usually occurs as inclusions within other minerals, such as spinel or pleonaste. Due to its size, its visual characteristics are difficult to observe without specialized equipment, such as a petrographic microscope. ## Physical Properties Magnesiohogbomite-6N6S crystals are characterized by a hardness of 6.5-7 on the Mohs scale. They have a vitreous to metallic luster. They are a dense mineral, with a density of approximately 3.81 g/cm³. They are usually opaque, rarely translucent. ## Colors and Varieties This mineral is most often black, dark brown, or reddish-brown. No color or commercial varieties are distinguished. ## History and Name The name "magnesiohogbomite" refers to the dominance of magnesium in its chemical composition and its association with the hogbomite group. The group name comes from the Swedish geologist Arvid Gustaf Högbom (1857-1940). The suffix "-6N6S" is part of the complex polysomatic nomenclature of the group, describing the stacking sequence of layers in the crystal structure.

Properties

Mohs hardness
6.5-7
Luster
Vitreous to metallic
Streak
Brown
Density
3.81
Cleavage
Imperfect on {0001}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Hexagonal

Diagnostic features

## Identification Identification of magnesiohogbomite-6N6S is extremely difficult and practically impossible without advanced analytical techniques. Under a petrographic microscope in transmitted light, it exhibits characteristic, strong pleochroism (color change) in shades from yellowish-brown to dark brown. Final confirmation requires methods such as X-ray microanalysis (EDS/WDS) or electron diffraction. ## Distinguishing from Similar Minerals It can be confused with other minerals from the hogbomite group, as well as with more common, dark rock-forming minerals like spinel, magnetite, ilmenite, or rutile. Differentiation is based on chemical composition analysis and optical properties under the microscope. ## Crystal Forms It forms small, hexagonal, tabular crystals, often with a prismatic habit. It usually occurs as single, isolated crystals within other minerals.

Geological environment

## Genesis This is a mineral typical of metamorphic rocks that have undergone transformation under conditions of high temperatures and pressures, corresponding to the amphibolite and granulite facies. It forms in rocks rich in aluminum and magnesium, and poor in silica, such as some gneisses, amphibolites, or calc-silicate rocks. ## Mineral Associations It most often coexists with spinel (especially its iron-rich variety - pleonaste), as well as with corundum, phlogopite, hornblende, chondrodite, clinohumite, and calcite. ## Localities Key confirmed localities include: Varpa mine in Sweden (type locality), the Bancroft area in Ontario (Canada), the Finero ultramafic complex in Italy, and the Tallgruvan iron ore deposit, also in Sweden.

Rarity

Very rare

For collectors

## Quality Criteria From a collector's perspective, magnesiohogbomite-6N6S is a mineral of interest mainly to specialized collectors of rare minerals or "systematic" collectors. Its value lies not in aesthetics, but in its rarity and scientific significance. The most desirable specimens are those where the crystals, despite their microscopic size, are well-formed and identified in association with other minerals from a given locality.

Care and storage

## Cleaning Specimens containing magnesiohogbomite-6N6S inclusions can be cleaned with a soft brush and distilled water. However, cleaning is usually not necessary, as this mineral is stable and occurs as an inclusion. ## What to Avoid Contact with strong acids should be avoided, as they could damage both the mineral itself and the surrounding rock matrix. There are no specific recommendations regarding light or temperature, as it is a durable mineral. ## Storage Storage does not require special precautions. Specimens should be protected from dust and mechanical damage by storing them in display boxes or cabinets.

Sources

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