Rynersonite

Chemical formula: CaTa<sup>5+</sup><sub>2</sub>O<sub>6</sub>

Rynersonite is a rare, brown or black oxide mineral of the pyrochlore group, containing calcium and tantalum, found in granitic pegmatites.

## Characteristics Rynersonite is a rare mineral of the pyrochlore group, belonging to the oxide class. Chemically, it is a calcium tantalum oxide, often with niobium admixture. It forms small, isometric (equant) crystals, typically octahedral in habit, which rarely exceed 1 mm in size. It also occurs as granular aggregates or as massive grains embedded in rock. ## Physical Properties This mineral is characterized by a hardness of approximately 5.5 on the Mohs scale. It has a high density, ranging from 6.4 to 6.5 g/cm³, which is typical for tantalum-bearing minerals. The luster of rynersonite is described as resinous to metallic. It is a brittle mineral with an uneven or conchoidal fracture. ## Colors and Varieties Its color is variable, from yellowish-brown, through reddish-brown, to black. In thin fragments, it may be translucent brown. No named varieties of this mineral are distinguished. ## History and Name The mineral is named in honor of Eugene

Properties

Mohs hardness
5.5
Luster
Resinous, Metallic
Streak
Light brown
Density
6.4 - 6.5
Cleavage
None
Fracture
Uneven, Conchoidal
Transparency
Translucent to opaque
Crystal system
Cubic

Diagnostic features

## Identification - Rynersonite is difficult to identify without advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). Its high density, hardness of approximately 5.5, and characteristic crystal habit (octahedral) can be indicative, but definitive identification requires instrumental analysis. It can be confused with other dark, dense oxide minerals found in pegmatites, especially other members of the pyrochlore supergroup or columbite-tantalite minerals. The presence of tantalum and calcium is key to its chemical identification.

Geological environment

## Genesis Rynersonite is a secondary mineral, forming in the weathering zones of granitic pegmatites, especially those rich in lithium and tantalum. It forms as a result of hydrothermal alteration or weathering of primary tantalum minerals, such as microlite or tapiolite. ## Mineral Associations It occurs in association with other pegmatitic minerals, such as quartz, albite, microcline, muscovite, lepidolite, spodumene, as well as other tantalum and niobium oxides, e.g., from the pyrochlore group (microlite, uranmicrolite) and columbite. ## Localities The main, confirmed occurrences of rynersonite include its type locality at the San Domingo mine in the Cahuilla district, Riverside County, California (USA). It is also found in other pegmatites worldwide, including Russia (Kola Peninsula), Brazil (Minas Gerais), Mozambique (Alto Ligonha), and the Czech Republic.

Rarity

Very rare

For collectors

## Quality Criteria As a rare mineral occurring in the form of small crystals, rynersonite is valued primarily for its documented presence in a collection. The most desirable specimens are those with well-formed, sharp crystals of a distinct, octahedral shape, embedded in a contrasting rock matrix, such as albite or quartz. A darker, saturated color and good luster also increase the specimen's value. Due to the microscopic size of the crystals, they are often offered in special micromount boxes. ## Popular Localities The most classic and sought-after specimens by collectors come from the type locality in California, USA. Specimens from other known localities, such as Russia or Mozambique, are also valued due to the mineral's rarity.

Care and storage

I

External references

Sources

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