Micheelsenite

Chemical formula: (Ca,Y)₃Al(PO₃OH)CO₃(OH)₆·12H₂O

Micheelsenite is a very rare mineral from the carbonate and phosphate group, forming colorless, hexagonal crystals, found in Canada.

## Characteristics Micheelsenite is a complex hydrated calcium, ytterbium, and aluminum carbonatophosphate. It occurs as small, hexagonal crystals, typically not exceeding 1 mm in length. The crystals are most often colorless and transparent, with a vitreous luster. Due to its rarity and small crystal size, it is a mineral primarily of scientific and collector interest. ## Physical Properties This mineral is characterized by a hardness of approximately 4 on the Mohs scale. It has a white streak and a vitreous luster. It is transparent. The density of micheelsenite has been calculated at 2.49 g/cm³. ## Colors and Varieties Micheelsenite is typically colorless. No colored varieties or commercial names have been reported. ## History and Name The mineral was discovered at the Poudrette quarry in Mont Saint-Hilaire, Quebec (Canada). It was described in 2003 by Ole V. Petersen, Joel D. Grice, Andrew C. Roberts, Robert A. Gault, Mark A. Cooper, and Frank C. Hawthorne. The name honors Harry Ingemann Micheelsen (1931–1999), a Danish mineralogist and crystallographer from the University of Copenhagen, in recognition of his contributions to mineralogy and optical crystallography. ## Uses Due to its extreme rarity and small crystal size, micheelsenite has no industrial applications. It is solely an object of scientific interest and is valued by specialized collectors of rare minerals.

Properties

Mohs hardness
3.5-4
Color
White to colourless
Luster
Vitreous
Streak
White
Density
2.15
Cleavage
<mi>{10_10}</mi> and {0001} good
Fracture
Splintery
Transparency
Transparent
Crystal system
Hexagonal

Diagnostic features

## Identification Micheelsenite is difficult to identify visually without specialized equipment. Its key features include its occurrence as small, colorless, hexagonal crystals with a vitreous luster. Identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). ## Distinguishing from Similar Minerals It can be confused with other colorless secondary minerals found in the same environment, such as calcite, quartz, or other rare phosphates and carbonates. Differentiation is based on the analysis of crystal shape (hexagonal with flat terminations) and confirmation of chemical composition. ## Crystal Forms It forms elongated, prismatic crystals with a hexagonal cross-section, terminated by flat pinacoids. Crystals are usually very small, rarely exceeding 1 mm in length.

Geological environment

## Genesis Micheelsenite is a secondary mineral, formed in the late stages of hydrothermal processes within alkaline nepheline syenite intrusions. It crystallizes in rock cavities and fissures from solutions rich in calcium, yttrium, aluminum, phosphorus, and carbonates. ## Mineral Associations It co-occurs with other rare minerals typical of the Mont Saint-Hilaire locality, such as aegirine, microcline, albite, calcite, natrolite, analcime, catapleiite, rosenbuschite-(Ce), and petersenite-(Ce). ## Localities The only confirmed locality for micheelsenite in the world is its type locality – the Poudrette quarry, Mont Saint-Hilaire, Montérégie region, Quebec, Canada.

Rarity

Very rare

For collectors

## Quality Criteria The quality of micheelsenite specimens is primarily assessed based on the size, sharpness, and transparency of the crystals. The most desirable are well-formed, sharply terminated, fully transparent crystals, set on a contrasting rock matrix. Due to their small size, a rich association with other rare minerals is also crucial. ## Popular Localities The only source of micheelsenite specimens is the Poudrette quarry in Mont Saint-Hilaire, Canada. This locality is world-renowned for hundreds of rare and unique minerals, and specimens from there are highly valued in systematic collections.

Care and storage

## Cleaning Micheelsenite specimens should be cleaned with the utmost care, using a soft brush to remove dust. Due to its fragility and potential reactivity, wet cleaning, especially with ultrasonics, should be avoided. ## What to Avoid Avoid contact with all chemicals, including acids and strong bases, which can damage or dissolve the mineral. Protect it from high temperatures, which can lead to dehydration and structural damage. Avoid shocks and impacts due to its fragility. ## Storage It is recommended to store micheelsenite specimens in stable conditions, in sealed "micromount" boxes, which protect them from dust, mechanical damage, and sudden changes in humidity. Avoid exposure to direct sunlight.

External references

Sources

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