Koragoite
Chemical formula: Mn<sup>2+</sup><sub>2</sub>Mn<sup>3+</sup>Nb<sup>5+</sup><sub>2</sub>(Nb<sup>5+</sup>,Ta<sup>5+</sup>)<sub>3</sub>W<sup>6+</sup><sub>2</sub>O<sub>20</sub>
Koragoite is an extremely rare, black oxide mineral containing manganese, niobium, and tungsten, known from only one locality in the world.
Description
## Characteristics Koragoite is a black mineral with a submetallic luster. It occurs as very small, anhedral grains, not exceeding 0.5 mm in size. Due to its nature, it does not form well-developed crystals visible to the naked eye and is found as inclusions in other minerals. ## Physical Properties This mineral is opaque. It has a Mohs hardness of 5.5 and a high density of approximately 6.45 g/cm³. It exhibits no cleavage, and its fracture is conchoidal. ## Colors and Varieties Koragoite has a uniform, black color. No color varieties or commercial forms are known. ## History and Name The mineral was approved by the IMA in 1997, and its description was published in 1998. The name comes from the discovery locality – the Korago massif in Krasnoyarsk Krai, Russia, which remains its only known occurrence. ## Applications Due to its extreme rarity and microscopic size, koragoite has no commercial or industrial applications. Its significance is purely scientific, and it is an object of interest for specialized collectors of micromount minerals.
Diagnostic features
## Identification Identification of koragoite is impossible without advanced analytical techniques. It requires chemical composition analysis (e.g., by EDS/WDS) to confirm the presence of manganese, niobium, tantalum, and tungsten. Visual characteristics, such as black color, submetallic luster, and high density, are non-specific. ## Distinguishing from Similar Minerals It is visually indistinguishable from many other black, heavy oxide minerals with which it co-occurs, such as columbite, ilmenite, or ferrowodginite. Only chemical analysis provides a definitive distinction. ## Crystal Forms Koragoite occurs exclusively as anhedral (irregular, lacking crystal faces) grains. No well-formed crystals have been observed.
Geological environment
## Genesis This mineral forms under hydrothermal or pegmatitic conditions. It was found in a quartz-plagioclase vein cutting a gabbro-diorite intrusion. ## Mineral Associations Koragoite co-occurs with other, often rare, minerals such as columbite-(Fe), columbite-(Mn), ilmenite, ferrowodginite, as well as scheelite, wolframite, cassiterite, and native bismuth. ## Localities The only confirmed locality for koragoite in the world is its type locality – the Korago massif, in the Sayan Mountains region, Krasnoyarsk Krai, Russia.
Rarity
Extremely rare
Collector aspects
## Quality Criteria For collectors, the value of a koragoite specimen lies not in the aesthetics of a single grain, which is microscopic, but in the confirmed presence of the mineral on the rock matrix. Samples with the largest possible number of koragoite grains and rich associations of other rare minerals are most highly prized. ## Popular Localities Specimens come exclusively from one locality in the world – the Korago massif in Russia, making them extremely difficult to acquire.
Care and storage
## Cleaning Koragoite specimens, typically microscopic grains within a host rock, should not be cleaned mechanically or chemically. Fine dust can be removed with a soft brush or a gentle stream of compressed air. ## What to Avoid Ultrasonic cleaners and any chemical agents should be strictly avoided, as they could damage not only the mineral itself but, more importantly, the host rock in which it is embedded. ## Storage It is recommended to store specimens in specialized "micromount" boxes, which protect against dust, moisture, and mechanical damage. Standard room conditions are sufficient.