Cancrinite

Chemical formula: (Na,Ca,&#₉₇₄₄;)₈(Al₆Si₆)O₂₄(CO₃,S₆+O₄)₂·₂H₂O

Cancrinite is a complex tectosilicate from the feldspathoid group, most often characterized by its yellow color and occurrence in nepheline syenites.

## Characteristics Cancrinite is a mineral belonging to the feldspathoid group, closely related to sodalite. It rarely forms well-developed, hexagonal, prismatic crystals. It usually occurs as compact, granular, or fibrous aggregates, embedded in the rock mass. Its crystals often have uneven, corroded surfaces. It is brittle and exhibits piezoelectric properties. ## Physical Properties This mineral is characterized by a hardness of 5-6 on the Mohs scale and a density ranging from 2.42 to 2.51 g/cm³. Cancrinite's luster is vitreous on crystal faces, and often greasy or pearly on fracture surfaces. It is transparent to translucent. Some specimens may exhibit orange fluorescence under ultraviolet light. ## Colors and Varieties Cancrinite most often takes on colors from lemon-yellow to orange. White, gray, greenish, bluish, or colorless specimens are also found. The variety of colors results from the presence of different impurities and inclusions. No named commercial varieties are distinguished, and classification is based mainly on chemical composition. ## History and Name The mineral's name comes from the surname of Count Georg Cancrin (1774-1845), a Russian Minister of Finance and mineralogy enthusiast. The mineral was first described in 1839 by Gustav Rose based on specimens found in the Ilmen Mountains in the Southern Urals, Russia. ## Uses Cancrinite has no significant industrial application. Its importance is limited mainly to the scientific and collecting spheres. It is valued by collectors for its intense, yellow coloration and the rarity of well-formed crystals.

Properties

Mohs hardness: 5-6
Luster: Vitreous, greasy, pearly
Streak: White
Density: 2.42-2.51
Cleavage: Perfect on {1010}
Fracture: Uneven, conchoidal
Transparency: Transparent to translucent
Crystal system: Hexagonal

Diagnostic features

## Identification The most important diagnostic feature of cancrinite is its violent reaction with hydrochloric acid, during which carbon dioxide is released, causing effervescence. Its characteristic lemon-yellow color, greasy luster on fracture, and co-occurrence with nepheline and sodalite in syenites are also distinctive. ## Distinguishing from Similar Minerals Cancrinite is sometimes confused with other yellow minerals. It is distinguished from **melilite** and **gehlenite** by its lower hardness and reaction with acid. It differs from **yellow quartz (citrine)** by its significantly lower hardness. It is distinguished from **yellow apatite** by the absence of apatite's characteristic hexagonal cross-section and lower hardness. Unlike **sodalite**, with which it often occurs, cancrinite is usually yellow, not blue, and reacts violently with acids. ## Crystal Forms Cancrinite crystals belong to the hexagonal system and have a prismatic or columnar habit, often terminated by a pyramid. They are usually poorly developed, with rounded edges. It is most often found in the form of compact, granular, fibrous, or radial aggregates.

Geological environment

## Genesis Cancrinite is a mineral of magmatic origin. It forms in the late stages of crystallization in alkaline, silica-poor igneous rocks, such as nepheline syenites and phonolites. It can also form as a result of hydrothermal processes, altering other minerals, mainly nepheline. It is also found in contact skarns. ## Mineral Associations This mineral typically co-occurs with other feldspathoids and alkaline rock minerals. It is most often accompanied by: nepheline, sodalite, microcline, sanidine, albite, biotite, aegirine, as well as calcite and natrolite. ## Localities The most important global localities for cancrinite are the Kola Peninsula and the Ilmen Mountains in the Urals, Russia. Significant specimens also come from Bancroft in Ontario (Canada), where large crystals occur, and from Langesundsfjorden in Norway. Other known occurrences include Magnet Cove in Arkansas (USA), the area around Lake Laacher in Germany, and Iporã in Goiás (Brazil).

Rarity

Not very common

For collectors

## Quality Criteria The most sought-after by collectors are well-formed, sharply terminated crystals with a prismatic habit. Specimens with intense, lemon-yellow or orange color, high transparency, and vitreous luster are highly valued. The attractiveness is also enhanced by the contrasting placement of yellow cancrinite crystals on a darker rock matrix, often accompanied by sodalite or aegirine. ## Popular Localities Localities in Russia (Kola Peninsula) and Canada (Bancroft area in Ontario) are considered classic and provide the best specimens. Canadian specimens are known for reaching considerable sizes, even up to several tens of centimeters, although they rarely have gemological quality. Specimens from Langesundsfjorden in Norway are also highly regarded by collectors.

Care and storage

## Cleaning Cancrinite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, a damp cloth can be used or the specimen can be rinsed in distilled water, then immediately dried. Ultrasonic cleaners should be avoided. ## What to Avoid Cancrinite is sensitive to acids – even weak acids, such as hydrochloric acid, cause it to effervesce violently and decompose. It should be protected from contact with household and laboratory chemicals. It is a brittle mineral, susceptible to mechanical damage. ## Storage Specimens should be stored in separate, padded boxes or display cases to prevent scratching by harder minerals. It is recommended to keep it away from sources of moisture and extreme temperatures.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCancrinite