Hydroxykenomicrolite
Chemical formula: (☐,Na,Sb<sup>3+</sup>)<sub>2</sub>Ta<sup>5+</sup><sub>2</sub>O<sub>6</sub>(OH)
Hydroxykenomicrolite is an extremely rare mineral from the pyrochlore supergroup, forming small, octahedral crystals with a high tantalum content.
Properties
- Mohs hardness
- 5
- Luster
- Adamantine, Resinous
- Streak
- Light brown
- Density
- 6.33
- Cleavage
- Indistinct on {111}
- Fracture
- Subconchoidal
- Transparency
- Translucent to opaque
- Crystal system
- Isometric
Diagnostic features
## Identification Features facilitating identification in a collection are: crystal habit (perfect octahedra), high density (the specimen is heavy for its size), resinous or adamantine luster, and occurrence environment (granitic pegmatites). However, final confirmation of identity requires advanced chemical analysis (e.g., EDS), as distinguishing it from other minerals in the microlite group is visually impossible. ## Distinguishing from Similar Minerals Hydroxykenomicrolite can be confused with other minerals from the pyrochlore supergroup (e.g., fluorocalciomicrolite, oxykenomicrolite), from which it differs in chemical composition. It can also be similar to small crystals of zircon, cassiterite, or sphalerite. Zircon is much harder (7.5), and cassiterite has a higher density and often a different crystal habit. ## Crystal Forms It most often forms single, euhedral (well-formed) crystals in the form of an octahedron {111}, less often a rhombic dodecahedron. Crystals are usually small, not exceeding a few millimeters in size.
Geological environment
## Genesis It is a secondary mineral, formed in the late stages of hydrothermal processes or as a result of metasomatism in zones of highly differentiated granitic pegmatites, especially of the LCT (lithium-cesium-tantalum) type. It forms as a result of alterations of primary tantalum minerals. ## Mineral Associations It most often co-occurs with other pegmatitic minerals, such as albite, lepidolite, elbaite, tantalite-(Mn), cassiterite, and other rare tantalum and niobium minerals. ## Localities The most important and type locality for hydroxykenomicrolite is the Muiâne pegmatite, in the Alto Ligonha district, Zambézia Province, Mozambique. It is also known from the Volta Grande pegmatite in Minas Gerais state, Brazil. Occurrences have also been reported in several other localities worldwide, but specimens from these are usually microscopic in size.
Rarity
Extremely rare
For collectors
## Quality Criteria The most highly prized specimens are those with sharp, fully formed, lustrous crystals of the largest possible size. Their placement on a contrasting matrix, such as white albite or purple lepidolite, is highly desirable, as it enhances the crystal's color and form. Purity and lack of damage are crucial. ## Popular Localities By far the most well-known and valued by collectors are specimens from the type locality in Muiâne, Mozambique. Most of the well-formed crystals available on the collector's market originate from there.
Care and storage
## Cleaning Hydroxykenomicrolite specimens should only be cleaned mechanically, 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 The mineral is sensitive to strong acids and bases. Contact with household and laboratory chemicals should be avoided. It should not be subjected to sudden temperature changes. ## Storage It is recommended to store specimens in separate, sealed collector boxes to protect them from dust and mechanical damage. It is stable and does not require protection from light.