Johnsenite-(Ce)

Chemical formula: Na₁₂Ce₃+₃Ca₆Mn₂+₃Zr₄+₃W₆+Si₂₅O₇₃(CO₃)(OH)₂

Johnsenite-(Ce) is an extremely rare mineral from the eudialyte group, characterized by a complex chemical composition and occurring as small, brown grains.

## Characteristics Johnsenite-(Ce) is a very rare, complex silicate belonging to the eudialyte supergroup. It occurs as small, anhedral or subhedral grains, rarely exceeding 1.5 mm in size. This mineral is transparent and has a vitreous luster. Its color ranges from light brown to brown. Due to its microscopic size and rarity, it is primarily of scientific interest and sought after by specialized collectors of microminerals. ## Physical Properties The hardness of johnsenite-(Ce) on the Mohs scale is 5. The mineral does not exhibit cleavage, and its fracture is conchoidal. The density calculated based on the chemical formula and unit cell parameters is approximately 3.05 g/cm³. ## Colors and Varieties This mineral forms crystals with a color ranging from light brown to brown. No color varieties or commercial varieties are known. ## History and Name Johnsenite-(Ce) was first described in 2005 by Joel D. Grice and Robert A. Gault. The mineral is named in honor of Ole Johnsen (born 1943), a Danish mineralogist and curator at the Geological Museum at the University of Copenhagen, for his contributions to the study of minerals from the eudialyte group. The suffix "-(Ce)" indicates that cerium is the dominant rare-earth element in its structure. ## Uses Johnsenite-(Ce) has no industrial applications. Its significance is purely scientific and for collectors.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 3.05
Cleavage: None
Fracture: Conchoidal
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification Amateur identification of johnsenite-(Ce) is practically impossible. It requires advanced analytical techniques, such as X-ray microanalysis (EDS/WDS), to confirm its complex chemical composition. Preliminary indications include its brown color, vitreous luster, lack of cleavage, and co-occurrence with other rare alkaline minerals. ## Distinguishing from Similar Minerals This mineral can be easily confused with other brown members of the eudialyte supergroup, such as eudialyte, kentbrooksite, or other minerals with similar compositions. Definitive differentiation is only possible through detailed chemical analysis, which will show the dominance of cerium and the presence of tungsten in the structure. ## Crystal Forms Johnsenite-(Ce) forms anhedral (irregular, shapeless) to subhedral (partially formed) grains. Well-formed, idiomorphic crystals have not yet been found.

Geological environment

## Genesis Johnsenite-(Ce) forms in nepheline syenite pegmatites. These are rare, alkaline igneous rocks, rich in elements such as zirconium, niobium, and rare-earth elements, while being poor in silica. ## Mineral Associations This mineral occurs in association with other rare minerals typical of the Mont Saint-Hilaire environment. The most common associated minerals are aegirine, albite, analcime, catapleiite, eudialyte, microcline, natrolite, and serandite. ## Localities The only confirmed locality of johnsenite-(Ce) in the world is its type locality – the Poudrette quarry at Mont Saint-Hilaire in Quebec, Canada. This is one of the most famous mineralogical sites in the world, known for the occurrence of hundreds of rare and unique minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria As a micromineral, the collector's value of johnsenite-(Ce) depends on several factors. The most important is certainty of identification, confirmed by a reliable laboratory. The size of the individual grain and its placement on the matrix are also important – specimens where the grain is well-isolated and contrasts with its surroundings are desirable. Associations with other rare, well-formed minerals are also highly valued. ## Popular Localities The only source of specimens is the Poudrette quarry at Mont Saint-Hilaire in Canada. Specimens from this locality are highly prized by specialized micromineral collectors.

Care and storage

## Cleaning Johnsenite-(Ce) specimens are typically very small grains on a rock matrix. They should be cleaned with utmost care, preferably using compressed air to remove dust. If necessary, a soft, dry brush can be used. Wet cleaning is discouraged due to the risk of damaging delicate mineral associations. ## What to Avoid Contact with acids and other chemicals that can damage the mineral should be strictly avoided. Ultrasonic cleaners and steam cleaning should not be used. Despite the lack of data on light sensitivity, it is advisable to avoid prolonged exposure to direct sunlight. ## Storage Specimens should be stored in stable conditions, in specialized "micromount" boxes that protect them from dust, moisture, and mechanical damage. Each specimen should be precisely labeled, including location and confirmed identification.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FJohnsenite-(Ce)