Calciohilairite

Chemical formula: CaZr₄+Si₃O₉·₃H₂O

Calciohilairite is a rare zirconium and calcium silicate, forming small, vitreous crystals with a complex structure, found in syenites.

## Characteristics Calciohilairite is a rare mineral from the silicate group, chemically a hydrated zirconium and calcium silicate. It occurs as very small, usually not exceeding 1 mm, prismatic or pseudo-octahedral crystals. Its crystals are characterized by a complex structure and numerous faces. It typically forms single, scattered crystals or small, radial aggregates embedded in the host rock. It is a transparent to translucent mineral with a vitreous luster. ## Physical Properties This mineral is relatively hard, with a Mohs hardness of approximately 4.5. It has a white streak and a vitreous luster. The density of calciohilairite is calculated at 2.83 g/cm³. It does not exhibit cleavage, and its fracture is uneven. ## Colors and Varieties Calciohilairite is most often colorless or white. Pale pink specimens are also found. No distinct varieties have been identified. ## History and Name The mineral's name refers to its chemical composition – the dominance of calcium (Latin: *calcius*) – and its structural similarity to hilairite. It was approved as a new mineral by the International Mineralogical Association (IMA) in 1990. It was first described based on material from the Poudrette quarry at Mont Saint-Hilaire in Quebec, Canada. ## Uses Due to its rarity and small crystal size, calciohilairite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and micromounts.

Properties

Mohs hardness: 4.5
Luster: Vitreous
Streak: White
Density: 2.83
Cleavage: None
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Trigonal

Diagnostic features

## Identification Amateur identification of calciohilairite is very difficult due to the small size of its crystals and its resemblance to other minerals. Its characteristic crystal form (trigonal prisms) and occurrence environment – nepheline syenites – are distinctive. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Distinguishing from Similar Minerals Calciohilairite can be confused with quartz, analcime, natrolite, or other zeolites that often co-occur with it. It is distinguished from them primarily by its unique crystal form and higher density. It is structurally related to hilairite, from which it differs by the dominance of calcium over sodium in its chemical composition. ## Crystal Forms It forms short, prismatic crystals with a hexagonal or trigonal outline, often terminated by steep rhombohedra, giving them a pseudo-octahedral appearance. It occurs as single, unattached crystals or in small, radial aggregates.

Geological environment

## Genesis Calciohilairite is a mineral of hydrothermal origin. It forms in the late stages of crystallization within pegmatites and miaroles in alkaline igneous rocks, such as nepheline syenites. It crystallizes from post-magmatic solutions rich in zirconium, calcium, and silica. ## Mineral Associations This mineral co-occurs with many other rare minerals typical of nepheline syenites. It is most commonly associated with: aegirine, microcline, analcime, natrolite, catapleiite, elpidite, rosenbuschite, and also hilairite. ## Localities The most important and well-known locality for calciohilairite is its type locality – the Poudrette quarry at Mont Saint-Hilaire, in the Montérégie region of Quebec, Canada. This is the site from which most of the best specimens of this mineral originate. It has also been reported in the Ilimaussaq alkaline complex in Greenland and on the Kola Peninsula in Russia (Khibiny Massif).

Rarity

Very rare

For collectors

## Quality Criteria The collector appeal of calciohilairite primarily depends on the crystal habit and size. The most prized specimens are sharp, well-formed, transparent, and colorless crystals that stand out clearly from the host rock. Due to their small size, specimens are almost exclusively offered as micromounts. Contrast with associated minerals, such as dark green aegirine, enhances the aesthetic value of the specimen. ## Popular Localities Undoubtedly, the most sought-after and classic source for collectors is Mont Saint-Hilaire in Canada. Specimens from this locality are considered exemplary for this mineral species.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Distilled water may be used, but prolonged soaking should be avoided. Due to the small size of the crystals, dry cleaning is the safest method. ## What to Avoid Avoid contact with acids and other aggressive chemicals. The mineral is sensitive to ultrasound, which can damage delicate crystals. It should not be heated or exposed to sudden temperature changes. ## Storage The best method for storing calciohilairite, especially micromounts, is in special membrane boxes or small perky boxes, which protect delicate crystals from mechanical damage and dust. It should be stored in stable conditions, away from moisture.

Sources

IMA Mineral List (CNMNC)