Hydroxycancrinite

Chemical formula: (Na,Ca,K)₈(Al₆Si₆O₂₄)(OH,CO₃)₂·₂H₂O

Hydroxycancrinite is a rare mineral from the cancrinite group, an hydrated aluminosilicate of sodium, calcium, and potassium, forming hexagonal crystals.

## Characteristics Hydroxycancrinite is a mineral belonging to the cancrinite group within the tectosilicate family. It typically occurs as hexagonal, prismatic crystals, which can be elongated or short and barrel-shaped. It also forms granular or massive aggregates. Crystals are usually small, rarely exceeding a few millimeters in length. ## Physical Properties This mineral is characterized by a hardness of approximately 5 on the Mohs scale. It has a vitreous luster, and a greasy or dull luster on fracture surfaces. It is transparent to translucent. Its density is approximately 2.42 g/cm³. ## Colors and Varieties Hydroxycancrinite is usually colorless or white. It can also take on shades of gray, bluish, greenish, or yellowish, depending on impurities. There are no named varieties of this mineral. ## History and Name The mineral's name comes from its chemical composition – it indicates the dominance of the hydroxyl (OH) group and its relation to cancrinite. It was first described in 1992 by J.D. Grice and G. Gault based on material from Mont Saint-Hilaire, Canada. ## Applications Due to its rarity and small crystal size, hydroxycancrinite has no industrial application. It is of purely scientific importance and is valued by collectors specializing in rare minerals and micromounts.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 2.42
Cleavage: Perfect on {1010}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Field identification of hydroxycancrinite is difficult due to its resemblance to other minerals of the cancrinite and sodalite groups. Key features include the hexagonal crystal shape and occurrence in specific geological environments (nepheline syenites). Definitive identification requires advanced analytical methods such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). ## Distinguishing from Similar Minerals Hydroxycancrinite can be confused with cancrinite, vishnevite, quartz, nepheline, or scapolite. It is distinguished from quartz by its lower hardness. Differentiation from other minerals of the cancrinite-sodalite group is almost exclusively possible based on chemical analysis, which shows the dominance of hydroxyl (OH) ions over carbonate (CO₃) ions. ## Crystal Forms Crystals have the form of hexagonal prisms, often terminated by pyramids or flat pinacoids. They can form radial, fibrous, or massive, granular aggregates.

Geological environment

## Genesis Hydroxycancrinite is an igneous mineral, crystallizing in the late stages from alkaline, silica-undersaturated melts. It also forms as a result of hydrothermal and metasomatic processes, altering earlier minerals such as nepheline. ## Mineral Associations It most commonly co-occurs with minerals typical of nepheline syenites and their pegmatites, such as nepheline, sodalite, microcline, albite, aegirine, as well as other minerals from the cancrinite group and rare alkaline minerals. ## Localities The most important and classic localities for this mineral are alkaline complexes. The most significant include: Mont Saint-Hilaire in Quebec (Canada) – the type locality, as well as the Khibiny and Lovozero massifs on the Kola Peninsula in Russia.

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, sharp, transparent, and undamaged crystals, clearly contrasting with the host rock, are most valued by collectors. Specimens from rare localities or with unusual coloration (e.g., bluish) are also desirable. Crystal size is a key factor, as most specimens are micromounts. ## Popular Localities Collectors most seek specimens from classic localities: Mont Saint-Hilaire in Canada, which provides some of the best crystals in the world, and from the alkaline massifs of the Kola Peninsula in Russia, known for their abundance of rare minerals.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Ultrasonic cleaners should not be used. ## What to Avoid The mineral is sensitive to acids, which can damage it. Contact with household and laboratory chemicals should be avoided. It should not be heated or exposed to sudden temperature changes. ## Storage Specimens, especially those with well-formed crystals, are fragile and should be stored in separate, padded boxes or display cases to prevent mechanical damage. Due to the small size of the crystals, storage as micromounts is popular.

Sources

IMA Mineral List (CNMNC)