Magnesionigerite-6<i>N</i>6<i>S</i>

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

An extremely rare, black mineral from the nigerite group, found exclusively in the Norwegian granite pegmatite in Kåbuland.

## Characteristics Magnesionigeryte-6N6S is a very complex oxide belonging to the nigerite supergroup. It is one of the rarest members of this group, identified as a distinct mineral species in 2003. It forms very small, tabular or short, hexagonal crystals, usually not exceeding 1 mm. It has a black color and a submetallic luster. ## Physical Properties The mineral is opaque. Its hardness and density have not yet been precisely measured due to the small size and rarity of the material. The luster is described as submetallic. ## Colors and Varieties Magnesionigeryte-6N6S occurs exclusively in black. No colored or commercial varieties are known. ## History and Name The mineral's name refers to its chemical composition – dominant magnesium (magnesio) – and its structural relationship to nigerite. The suffix "6N6S" describes a specific, ordered sequence of alternating layers with nolanite (N) and spinel (S) structures in its crystal lattice. It was approved by the International Mineralogical Association (IMA) in 2003. The type locality, or place of discovery, is the Kåbuland pegmatite in Norway. ## Applications Due to its extreme rarity and microscopic size, magnesionigeryte-6N6S has no commercial or industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized micromineral collectors.

Properties

Luster
Sub-metallic
Streak
Greyish green
Transparency
Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Identification is extremely difficult and practically impossible without advanced analytical techniques. Visual features, such as black color, submetallic luster, and hexagonal, tabular crystals, are non-specific. The geological context (granite pegmatite) and associated minerals are crucial. Definitive identification requires chemical composition analysis (EDS) and crystal structure analysis (XRD). ## Distinguishing from Similar Minerals Magnesionigeryte-6N6S can be confused with other black, opaque pegmatitic minerals, such as cassiterite, columbite, tantalite, ilmenite, and especially with other minerals from the nigerite and spinel groups (e.g., gahnite, hercynite). Differentiation with the naked eye is impossible. It differs from them by its unique chemical composition (simultaneous presence of Mg, Al, Zn, and Sn) and specific crystal structure. ## Crystal Forms It forms small, hexagonal crystals with a tabular to short-prismatic habit, often occurring in small aggregates.

Geological environment

## Genesis It is a magmatic mineral, crystallizing in the late stage of the evolution of granite pegmatites, rich in rare elements. ## Mineral Associations In the type locality (Kåbuland), it co-occurs with quartz, plagioclase, muscovite, beryl, schorl (black tourmaline), cassiterite, columbite-(Fe), and gahnite. ## Localities The only confirmed occurrence of magnesionigeryte-6N6S in the world is the Kåbuland pegmatite in the Iveland district, Agder region, Norway.

Rarity

Extremely rare

For collectors

## Quality Criteria For such a rare micromineral, the most important criterion is the crystal's development and sharpness of edges, even if it is sub-millimeter. Specimens with clear, undamaged crystals embedded in a rock matrix, especially in association with other rare minerals, are highly valued. Size, though always desirable, is of secondary importance in this case. ## Popular Localities The only source of specimens is the type locality – the Kåbuland pegmatite in Norway. Material from this location is extremely difficult to acquire.

Care and storage

## Cleaning Specimens should be cleaned with the utmost care, preferably using canned compressed air or a very soft brush (e.g., squirrel hair) to remove dust. Due to the small size of the crystals, mechanical cleaning is not recommended. Washing in water, especially distilled water, should be a last resort, and the specimen should be thoroughly dried afterward. ## What to Avoid Contact with any chemicals, including acids and bases, should be strictly avoided. Ultrasonic cleaners are too aggressive and can damage delicate crystals. High temperatures and thermal shock should also be avoided. ## Storage The safest way to store specimens is to place them in a sealed "micromount" box with an appropriate label. This protects the mineral from dust, mechanical damage, and, most importantly, from being lost.

Sources

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