Parisite-(La)

Chemical formula: CaLa<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>F<sub>2</sub>

A rare mineral from the parisite group, the lanthanum analog of parisite-(Ce), forming small, hexagonal crystals of a brownish color.

## Characteristics Parisite-(La) is a very rare carbonate mineral belonging to the parisite series. It is the lanthanum analog of the much more common parisite-(Ce), meaning that lanthanum predominates over cerium in its chemical structure. It forms elongated, hexagonal crystals, often terminated by pyramids. It usually occurs as very small, individual crystals or small clusters, rarely exceeding a few millimeters in length. Its small size and rarity make it a mineral of interest mainly to specialized collectors and scientists. ## Physical Properties Parisite-(La) crystals are characterized by a vitreous or resinous luster. They are translucent to opaque. The Mohs hardness is approximately 4.5, and the density is relatively high, approximately 4.39 g/cm³, which is typical for minerals containing rare earth elements. It exhibits distinct cleavage in one direction. ## Colors and Varieties This mineral most often takes on a yellowish-brown to reddish-brown color. Due to its extreme rarity, no color varieties or commercial varieties are distinguished. ## History and Name The name "parisite-(La)" refers to its connection with parisite and the dominance of lanthanum (La) in its chemical composition. The basic name "parisite" comes from the name of J.J. Paris, owner of the Muzo emerald mine in Colombia, where parisite-(Ce) was first found. The suffix -(La) was added according to the rules for naming minerals with a dominant rare earth element, to distinguish it from other members of the series. ## Uses Due to its extreme rarity and small crystal size, parisite-(La) has no industrial applications. Its significance is purely scientific and for collectors.

Properties

Mohs hardness
4.5
Luster
Vitreous to resinous
Streak
White
Density
4.39
Cleavage
Distinct on {0001}
Fracture
Subconchoidal
Transparency
Translucent to opaque
Crystal system
Hexagonal

Diagnostic features

## Identification Amateur identification of parisite-(La) is practically impossible and requires advanced analytical methods, such as energy-dispersive spectroscopy (EDS) or X-ray diffraction (XRD), to confirm the dominance of lanthanum over cerium. Preliminary indications may include the hexagonal crystal form, brownish color, and high density, as well as its occurrence in a specific geological environment (carbonatites, nepheline pegmatites). ## Distinguishing from Similar Minerals It can be confused with other minerals from the parisite group, mainly parisite-(Ce) and synchysite-(La). Differentiation from parisite-(Ce) is only possible through chemical analysis. Synchysite-(La) has a very similar composition and appearance but differs in crystal structure, which can only be determined by diffraction methods. Visually, it may also resemble some small crystals of monazite or bastnäsite. ## Crystal Forms It most often forms simple, elongated, pyramidal or tabular crystals with a hexagonal cross-section. It occurs as single, small crystals or in small, radial aggregates.

Geological environment

## Genesis Parisite-(La) is a hydrothermal mineral, crystallizing in the late stages of the formation of certain types of igneous rocks. It is most commonly found in carbonatites and nepheline-syenite pegmatites, where it forms as a result of the concentration of rare earth elements, especially lanthanum. ## Mineral Associations It co-occurs with other rare earth element minerals and minerals typical of carbonatites and alkaline pegmatites. The most common associations include: ewaldite, mckelveyite-(Y), burbankite, calcite, quartz, microcline, and other REE carbonates, such as synchysite and bastnäsite. ## Localities This is an extremely rare mineral. It has been identified in several locations worldwide. The most important localities are: - New Ewald Mine, St. Andreasberg, Harz, Germany (type locality). - Green River Formation in Wyoming, USA. - Alkaline and carbonatite complexes, such as Mont Saint-Hilaire in Quebec, Canada, and on the Kola Peninsula in Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria For collectors, the most important criterion is the size and quality of crystal development. Specimens with sharp, well-defined, undamaged crystals are sought after, even if they are small (millimeter-sized). A distinct hexagonal form and luster increase value. Specimens on a rock matrix, especially in association with other rare minerals, are much more prized than isolated crystals. ## Popular Localities The most well-known specimens, though still microscopic in size, come from the historic locality in the Harz Mountains in Germany and from the Green River Formation in the USA. Specimens from Mont Saint-Hilaire in Canada are also valued by specialized collectors of rare minerals.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to possible reactivity with acids, all chemical cleaning agents should be avoided. If liquid is necessary, distilled water is recommended. ## What to Avoid Contact with acids (e.g., hydrochloric acid), which can damage or completely dissolve the mineral, must be absolutely avoided. Parisite-(La) is relatively soft, so it should be protected from scratching by harder minerals (quartz, beryl). It should not be heated or subjected to ultrasound. ## Storage It is recommended to store specimens in separate, padded display boxes to avoid abrasions and mechanical damage. Protect from dust and chemicals. Exposure to strong light is not considered harmful, but as with many rare minerals, caution is advised.

External references

Sources

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