Kimrobinsonite
Chemical formula: Ta<sup>5+</sup>(OH)<sub>3</sub>(O,CO<sub>3</sub>)
An extremely rare tantalum mineral with a habit of microscopic, cubic crystals, found exclusively in the Tanco pegmatite in Canada.
Description
## Characteristics Kimrobinsonite is a hydrated tantalum oxycarbonate, forming very small but well-formed crystals. They typically have a cubic form, not exceeding 0.1 mm in size. It occurs as single crystals, aggregates thereof, as well as anhedral grains and as coatings and crusts on other tantalum minerals. It ranges in color from pale yellow, through intense yellow, to orange-yellow, and is characterized by a strong, adamantine luster. ## Physical Properties The mineral's luster is adamantine. Crystals are translucent to opaque. The fracture is conchoidal. Due to the microscopic size of the crystals, hardness has not been precisely determined. The density calculated based on chemical composition and unit cell parameters is approximately 6.35 g/cm³. ## Colors and Varieties This mineral occurs in shades of yellow – from very light and pale to saturated, orange-yellow colors. No varieties have been distinguished. ## History and Name Kimrobinsonite was recognized as a new mineral species by the International Mineralogical Association (IMA) in 1983, and its full description was published in 1984. The name honors Dr. George Willard Robinson (born 1946), an American mineralogist and curator of the A. E. Seaman Mineral Museum in Houghton (Michigan, USA), in recognition of his contributions to mineralogy. ## Applications Due to its extreme rarity and microscopic size, kimrobinsonite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals (so-called microminerals).
Diagnostic features
## Identification Identification of kimrobinsonite is impossible without advanced analytical techniques. Due to its microscopic size, it requires the use of a scanning electron microscope with an EDS or WDS analyzer to confirm its chemical composition (dominance of tantalum, presence of hydroxyl and carbonate groups). X-ray diffraction (XRD) is also helpful for determining the crystal structure. A preliminary indication may be the cubic form of the crystals and adamantine luster in association with other tantalum minerals. ## Distinguishing from Similar Minerals Kimrobinsonite can be easily confused with other yellow or brown tantalum minerals found in the same environment, especially minerals from the microlite group. Microlite also crystallizes in the isometric system and often has a similar color, making visual distinction impossible. Definitive differentiation requires chemical analysis. ## Crystal Forms It forms very small, sharp cubic crystals, often with edges modified by other, less developed faces. It also occurs as irregular grains and aggregates, as well as thin coatings on other minerals.
Geological environment
## Genesis Kimrobinsonite forms in the late stages of crystallization in complex, highly differentiated LCT-type (lithium, cesium, and tantalum-rich) granitic pegmatites. It is a secondary or hydrothermal mineral, forming as a result of alterations of earlier tantalum minerals in an environment rich in water and carbon dioxide. ## Mineral Associations This mineral co-occurs with other, often rare, tantalum and lithium minerals. Its typical associations include wodginite, tantalite-(Mn), minerals from the microlite group, simpsonite, and beryllonite. ## Localities The only confirmed locality of kimrobinsonite in the world is its type locality – the Tanco mine, located on Bernic Lake in Manitoba, Canada. This is one of the world's most famous pegmatite deposits rich in rare elements.
Rarity
Extremely rare
Collector aspects
## Quality Criteria The quality of a kimrobinsonite specimen, being a micromineral, is assessed by different criteria than for macroscopic specimens. Specimens with sharp, well-formed, single cubic crystals that are clearly exposed on the rock matrix are most highly valued. The size of the crystal (even if it is a fraction of a millimeter), its intense color, and aesthetic association with other rare minerals are also important. ## Popular Localities The only source of kimrobinsonite specimens is the Tanco mine in Canada. Specimens from this locality are the standard for this mineral.
Care and storage
## Cleaning Kimrobinsonite specimens are almost exclusively microminerals, which are very delicate. Cleaning is not recommended. If dust removal is necessary, a stream of compressed air can be used very carefully from a safe distance. Avoid contact with water and any chemical agents. ## What to Avoid The mineral is sensitive to any mechanical shocks and abrasions. It should be protected from contact with chemicals, acids, and detergents. It should not be subjected to ultrasonic cleaning. ## Storage Specimens should be stored exclusively in specialized micromount boxes, with an appropriate label. Protect from dust, vibrations, and direct contact with other minerals.