Ankangite

Chemical formula: Ba(Ti,V<sup>3+</sup>,Cr<sup>3+</sup>)<sub>8</sub>O<sub>16</sub>

Ankangite is a rare barium, titanium, vanadium, and chromium oxide, forming microscopic, prismatic crystals of black color and metallic luster.

## Characteristics Ankangite is a very rare mineral from the hollandite group, belonging to the oxide class. It typically forms very small, prismatic or acicular crystals, not exceeding 0.1 mm in length, which can occur as radial aggregates. It is an opaque mineral, black in color with a black streak. ## Physical Properties Ankangite is characterized by a metallic luster. Its Mohs hardness ranges from 7 to 8, making it a hard mineral. The density calculated based on the chemical formula and unit cell parameters is 4.93 g/cm³. ## History and Name The mineral was discovered in the Shiquan deposit in Ankang Prefecture (Shaanxi Province, China), from which its name is derived. It was first described in 1986 by Shi Nicheng, Ma Zhesheng, and Peng Zhizhong and approved by the International Mineralogical Association (IMA) under number IMA1985-025. The type specimen is preserved at the Geological Museum of China in Beijing.

Properties

Mohs hardness
7-8
Luster
Metallic
Streak
Black
Density
4.93
Cleavage
Good on {110}
Fracture
Uneven
Transparency
Opaque
Crystal system
Tetragonal

Diagnostic features

## Identification Identification of ankangite is possible almost exclusively using advanced laboratory methods, such as chemical analysis (EDS) and X-ray diffraction (XRD). Visually, at the site of occurrence, it can be suspected based on its black color, metallic luster, and occurrence in a characteristic geological environment, in association with baryte, phlogopite, and quartz. ## Distinguishing from Similar Minerals Ankangite is visually indistinguishable from other black, metallic minerals of the hollandite group, such as hollandite, mannardite, or redledgeite. Definitive differentiation requires chemical composition analysis, particularly verification of the dominance of barium, titanium, and vanadium at the appropriate positions in the crystal structure. ## Crystal Forms Ankangite crystals are very small, with prismatic or acicular habit. They often form radial or disordered aggregates within the host rock.

Geological environment

## Genesis Ankangite forms under metamorphic conditions. In its type locality (Shiquan, China), it occurs in barium- and vanadium-rich phlogopite-quartzite layers that have undergone amphibolite facies metamorphism. Its formation is associated with hydrothermal or metasomatic activity within sedimentary rocks containing volcanic tuffs. ## Mineral Associations This mineral coexists with baryte, phlogopite, quartz, celsian, tourmaline (from the dravite-uvite group), titanite, rutile, apatite, pyrite, and chalcopyrite. ## Localities The only confirmed and thoroughly described occurrence of ankangite in the world is its type locality: the Shiquan deposit, near Ankang city, Shaanxi Province, China.

Rarity

Very rare

For collectors

## Quality Criteria As a microscopic mineral, ankangite is not evaluated according to typical criteria such as size or transparency. The collector's value of a specimen primarily depends on the richness and good development of microcrystals visible under magnification. Most desirable are samples with distinct, radial aggregates of acicular crystals on a contrasting host rock background. Certainty of identification, preferably confirmed by analysis, is also crucial.

Care and storage

## Cleaning Due to the microscopic size of the crystals and their occurrence within the host rock, mechanical cleaning of individual specimens is practically impossible and not recommended. Specimens on matrix can be cleaned of dust using compressed air or a soft brush. ## What to Avoid Avoid contact with strong acids, which could damage both ankangite and associated minerals. There is no detailed data on sensitivity to light or temperature, but standard caution is advised. ## Storage Ankangite specimens, as microminerals on rock matrix, should be stored in stable conditions, away from dust and chemical contaminants. The best solution is sealed "micromount" boxes, which protect delicate crystals and allow for their observation under a microscope.

Sources

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