Kenomicrolite

Chemical formula: &#₉₇₂₃;₂Ta⁵⁺₂[O₄(OH)₂]&#₉₇₂₃;

Kenomikrolite is a rare mineral from the pyrochlore supergroup, an oxide of tantalum, characterized by a vacancy at the A-cation site.

## Characteristics Kenomikrolite is a mineral of the microlite group, belonging to the pyrochlore supergroup. Its name refers to the dominant vacancy (Greek: *kenos* - empty) at the A-site in the crystal structure and the dominance of tantalum at the B-site. It typically forms small, well-formed crystals with an octahedral habit, often with modified faces. Specimens are most commonly found as fine, disseminated grains in the host rock. ## Physical Properties Kenomikrolite is characterized by a hardness in the range of 5-6 on the Mohs scale. It has a high, vitreous to resinous luster. It is a brittle mineral, with an uneven or conchoidal fracture. Its density is significant, approximately 6.78 g/cm³, which is typical for tantalum-rich minerals. ## Colors and Varieties This mineral occurs in various colors, most often yellow, yellowish-green, greenish-brown to brown. Its color depends on trace element impurities. There are no named commercial or color varieties. ## History and Name The name "kenomikrolite" was introduced in 2010 by the International Mineralogical Association (IMA) as part of the revision of the pyrochlore supergroup nomenclature. It replaced historical names for microlites with a vacancy at the A-site. The name comes from the Greek word *kenos* meaning "empty," referring to the vacancy at the A-cation site, and a reference to the microlite group. ## Uses Due to its rarity and small crystal size, kenomikrolite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and scientists studying pegmatites and minerals of the pyrochlore supergroup.

Properties

Mohs hardness: 6-0
Color: pale orange
Luster: Vitreous to resinous
Streak: white
Density: 5.599
Cleavage: Imperfect/indistinct on {111}
Fracture: Conchoidal
Transparency: Transparent
Crystal system: Isometric

Diagnostic features

## Identification Field identification of kenomikrolite is practically impossible without advanced analytical methods. In a collection, it can be suspected based on crystal habit (octahedra), high density, vitreous luster, and occurrence in granitic pegmatites. Definitive identification requires chemical analysis (EDS/WDS) to confirm tantalum dominance and a vacancy at the A-site. ## Distinguishing from Similar Minerals Kenomikrolite is visually indistinguishable from other minerals of the microlite group (e.g., fluoromicrolite, hydroxymicrolite) and pyrochlore. The differences lie in the chemical composition – the dominant cation at the A-site and the anion at the Y-site. It can also be confused with other minerals of similar habit and color, such as garnets, zircon, or some spinels, from which it is distinguished by its significantly higher density. ## Crystal Forms Kenomikrolite crystallizes in the isometric system, forming characteristic, well-developed crystals in the form of octahedra {111}. Crystal faces may be modified by other forms, giving them a more complex appearance. It also occurs as irregular grains and anhedral aggregates.

Geological environment

## Genesis Kenomikrolite is a mineral of magmatic origin, typical of granitic pegmatites, especially those with an advanced degree of fractionation, rich in lithium, cesium, and tantalum (LCT-type pegmatites). It forms in the late stages of crystallization from residual, rare-element-rich fluids and melts. ## Mineral Associations This mineral co-occurs with other pegmatitic minerals, such as quartz, albite (especially cleavelandite), lepidolite, spodumene, elbaite, beryl, cassiterite, columbite-(Mn) (manganocolumbite), and other minerals from the pyrochlore supergroup. ## Localities Kenomikrolite has been identified in many pegmatites worldwide. Important localities include: Tanco Mine in Bernic Lake, Manitoba (Canada); pegmatites in the Minas Gerais region (Brazil); Varuträsk pegmatite (Sweden); Londonderry Mine (Western Australia); and numerous localities in the USA, including San Diego County (California) and Oxford County (Maine).

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with sharp, well-formed crystals of intense, attractive color (e.g., vivid yellow or green) and strong luster. Crystal size is also important – specimens exceeding a few millimeters are rare. Crystals embedded in a contrasting matrix, such as white albite or purple lepidolite, are highly prized. ## Popular Localities Specimens from classic localities, such as the Tanco Mine in Canada, the Varuträsk pegmatite in Sweden, or the Mawi area in Afghanistan, are particularly sought after due to their historical and scientific significance.

Care and storage

## Cleaning Kenomikrolite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used. Ultrasonic cleaners should be avoided, as they can cause cracks in brittle crystals. ## What to Avoid This mineral is sensitive to strong acids and bases. Sudden temperature changes and prolonged exposure to direct sunlight should be avoided, although there is no evidence of fading. As a brittle mineral, it is susceptible to mechanical damage. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratches and impacts. They should be protected from dust and moisture. Due to the small size of the crystals, "micromount" type boxes are ideal.

External references

https://www.mindat.org/min-472197.html