Calkinsite-(Ce)

Chemical formula: Ce<sup>3+</sup><sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>·4H<sub>2</sub>O

Calkinsite-(Ce) is a rare, hydrated cerium carbonate, forming tiny, white or yellowish crystals and aggregates, usually in association with other rare earth minerals.

## Characteristics Calkinsite-(Ce) is a hydrated rare earth element carbonate with dominant cerium. It most often occurs as small, tabular or bladed crystals, which rarely exceed a few millimeters in length. These crystals often form rosette-like or radial aggregates, as well as thin coatings and earthy masses. Due to the small size of the crystals, its macroscopic features are difficult to observe without magnification. ## Physical Properties This mineral is characterized by relatively low hardness, 2.5 on the Mohs scale, which means it can be scratched with a fingernail. It has a vitreous to pearly luster, especially visible on cleavage surfaces. It is a light mineral, with a density of about 3.28 g/cm³. It is transparent to translucent. ## Colors and Varieties Calkinsite-(Ce) is typically white, yellowish, pale yellow, or yellowish-green. No named varieties are distinguished. ## History and Name The mineral was first described in 1953 by William T. Pecora and Joe H. Kerr. The name "calkinsite" honors Frank Cathcart Calkins (1878-1974), an American geologist working for the United States Geological Survey (USGS). The suffix "-(Ce)" was added later according to mineral nomenclature rules to indicate that cerium is the dominant rare earth element in its chemical composition. The type locality is the Bearpaw Mountains in Hill County, Montana, USA. ## Uses Calkinsite-(Ce) has no industrial application. Its significance is purely scientific and as a collector's item, as a rare representative of the rare earth carbonate group.

Properties

Mohs hardness
2.5
Color
pale yellow
Luster
Vitreous to Pearly
Streak
White to yellowish white
Density
3.28
Cleavage
{010} perfect, {101} distinct
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Field identification of Calkinsite-(Ce) is practically impossible without specialized equipment. In a collection, it is recognized based on its characteristic association with other rare earth carbonate minerals (e.g., lanthanite, ancylite) in carbonatites. Small, tabular crystals with a yellowish color and pearly luster are an indicative feature, but definitive identification requires chemical (EDS) and X-ray (XRD) analyses. ## Distinguishing from Similar Minerals It can be confused with other secondary REE carbonates, such as lanthanite-(Ce) or ancylite-(Ce). Lanthanite-(Ce) has a similar appearance but crystallizes in the orthorhombic system and often has a stronger pearly luster. Ancylite-(Ce) is harder (4-4.5) and denser. Final distinction is only possible using analytical methods. ## Crystal Forms It forms thin, tabular crystals with a hexagonal outline, often elongated, creating bladed forms. These crystals group into rosettes, radial aggregates, as well as lamellar and earthy masses.

Geological environment

## Genesis Calkinsite-(Ce) is a secondary mineral, forming in the weathering zones of carbonatites and other igneous rocks rich in rare earth elements. It forms as a result of the alteration of primary REE minerals, such as burbankite or ancylite, under the influence of surface waters saturated with carbon dioxide. ## Mineral Associations It most often co-occurs with other carbonates and REE minerals. Typical associated minerals include lanthanite-(Ce), ancylite-(Ce), burbankite, barite, calcite, dolomite, goethite, and quartz. ## Localities The most important and classic localities for this mineral are in the USA, in the Bearpaw Mountains in Montana (type locality). It is also known from carbonatites on the Kola Peninsula in Russia (Khibiny and Kovdor massifs), from the St. Honoré complex in Quebec, Canada, and from several other, rare localities worldwide where carbonatites occur.

Rarity

Rare

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, sharp crystals forming aesthetic rosettes or radial aggregates. A distinct yellow color and a contrasting matrix are important. Since the crystals are usually very small, micromount specimens are standard. Large aggregates visible to the naked eye are rare and highly prized. ## Popular Localities The best quality specimens, serving as a standard for this mineral, come from the type locality in the Bearpaw Mountains, Montana, USA. Specimens from Russia (Kola Peninsula) also provide collector material, although often with less visual appeal.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its low hardness and possible reactivity with acids, contact with chemicals should be avoided. The use of water, especially distilled water, should be kept to a minimum and performed with great caution. ## What to Avoid Avoid ultrasonic cleaners, chemical agents (especially acids, which can dissolve it), high temperatures, and prolonged exposure to moisture. The mineral is very soft and brittle, susceptible to mechanical damage. ## Storage Calkinsite-(Ce) specimens are best stored in separate, padded collector's boxes to protect them from scratching and impact. They should be protected from dust and moisture.

External references

Sources

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