Nioboixiolite-(Mn^2+^)

Chemical formula: (Nb<sup>5+</sup><sub>0.67</sub>Mn<sup>2+</sup><sub>0.33</sub>)O<sub>2</sub>

Nioboixiolite-(Mn²⁺) is a rare, black oxide mineral from the ixiolite group, containing niobium and manganese.

## Characteristics Nioboixiolite-(Mn²⁺) is a rare mineral from the ixiolite group, belonging to the oxide class. Chemically, it is a niobium and manganese oxide. It typically forms granular aggregates or poorly developed, prismatic crystals of small size, often occurring as inclusions in other minerals. It is opaque, black in color, and has a resinous to metallic luster. ## Physical Properties This mineral is characterized by high hardness, ranging from 6-6.5 on the Mohs scale, and significant density, reaching 5.91 g/cm³. It is brittle, and its fracture is uneven to conchoidal. The luster is most often resinous, but can also be metallic or submetallic. ## Colors and Varieties Nioboixiolite-(Mn²⁺) occurs in a uniform, black color. No color or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – the dominance of niobium (Niobo-), and its relation to the ixiolite structure (-ixiolite). The -(Mn²⁺) suffix specifies that manganese is the dominant divalent cation in this particular mineral. It was formally described as a new mineral species in 1999. ## Uses Due to its rarity and occurrence in small quantities, nioboixiolite-(Mn²⁺) has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and for scientists.

Properties

Mohs hardness
6-6.5
Luster
Pitchy to submetallic
Streak
Black
Density
5.91
Cleavage
Imperfect on {010}
Fracture
Uneven to conchoidal
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Amateur identification of nioboixiolite-(Mn²⁺) is practically impossible. It requires advanced analytical methods, such as chemical composition analysis (EDS/WDS) and X-ray diffraction (XRD). It can be tentatively suspected based on its black color, resinous luster, high hardness and density, and occurrence in granitic pegmatites. ## Distinguishing from Similar Minerals This mineral is visually indistinguishable from other black, heavy pegmatite minerals, such as columbite, tantalite, wolframixiolite, or samarskite. Definitive differentiation is only possible through specialized laboratory tests. ## Crystal Forms It most often occurs as anhedral (undeveloped) grains or subhedral (poorly developed) prismatic crystals. Crystals are usually small, rarely exceeding a few millimeters.

Geological environment

## Genesis Nioboixiolite-(Mn²⁺) is a mineral of magmatic origin. It forms in the late stages of crystallization in complex granitic pegmatites, especially those enriched in lithium, cesium, and tantalum (LCT type). ## Mineral Associations It often co-occurs with other pegmatite minerals, such as quartz, albite, microcline, muscovite, lepidolite, as well as rarer niobium and tantalum minerals, e.g., columbite-(Mn), tantalite-(Mn), microlite, cassiterite, and beryl. ## Localities The most important and well-documented occurrences of this mineral worldwide include pegmatites in the Mâncio Lima region in Acre, Brazil; the Viitaniemi pegmatite in Finland; the Tanco Mine in Bernic Lake, Manitoba (Canada); and pegmatites in the Alto Ligonha region in Mozambique.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of a nioboixiolite-(Mn²⁺) specimen primarily depends on its documented provenance and analytically confirmed identity. Specimens with well-formed, even if partially, crystals are most valued. Association with other rare pegmatite minerals is also important, as it enhances the contextual value of the specimen. ## Popular Localities Specimens from classic localities, such as Viitaniemi in Finland or the Tanco Mine in Canada, are particularly sought after by specialized collectors due to their scientific and historical significance.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush or paintbrush to remove dust. Due to its rarity and potential co-occurrence with sensitive minerals, contact with water and chemical agents should be avoided. ## What to Avoid Ultrasonic cleaners and all acids and bases should be avoided, as they could damage the mineral's surface or associated minerals. It should not be heated or exposed to sudden temperature changes. ## Storage Nioboixiolite-(Mn²⁺) specimens are best stored in stable conditions, in a closed display box, to protect them from dust and mechanical damage. It is advisable to isolate it from other minerals to prevent scratching.

Sources

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