Cancrisilite

Chemical formula: Na₇(Si₇Al₅)O₂₄(CO₃)·₃H₂O

A rare silicate from the cancrinite group, forming colorless or pale, hexagonal crystals in nepheline syenite pegmatites.

## Characteristics Cancrisilite is a complex sodium and aluminum silicate from the cancrinite group, belonging to the tectosilicate class. It forms elongated, hexagonal crystals of prismatic habit, terminated by pyramids. It also occurs as granular aggregates or as fillings in small veins. It is a brittle mineral. ## Physical Properties Cancrisilite has a hardness of 5 on the Mohs scale. It exhibits a vitreous luster on crystal faces and fracture surfaces. It is transparent to translucent. Its density is approximately 2.42 g/cm³. It shows perfect cleavage in one direction, parallel to the prism faces. ## Colors and Varieties This mineral is most often colorless, white, or takes on a pale, bluish tint. No distinct color varieties or commercial varieties are recognized. ## History and Name Cancrisilite was first described in 1991 by A.P. Khomyakov, G.N. Nechelyustov, and R.K. Rastsvetaeva. Its name refers to its structural and chemical similarity to cancrinite and to its higher silica content (Latin: *silex*) compared to other minerals in this group. ## Uses Due to its rarity, cancrisilite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced systematic and regional mineral collections.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 2.42
Cleavage: Perfect on {10-10}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Cancrisilite is identified by its characteristic crystal form – hexagonal, prismatic columns. The occurrence environment (pegmatites in alkaline massifs) and associated minerals such as nepheline, sodalite, or aegirine are also crucial. It possesses perfect prismatic cleavage. ## Distinguishing from Similar Minerals Cancrisilite is visually almost impossible to distinguish from cancrinite and vishnevite without advanced laboratory analysis (chemical analysis, X-ray diffraction). It can also be confused with some colorless zeolites, such as natrolite, however, natrolite usually forms acicular or fibrous crystals. It is distinguished from quartz by its lower hardness. ## Crystal Forms Cancrisilite crystals have a habit of hexagonal, elongated columns (prisms), often terminated by pyramid faces. It also occurs as granular aggregates and as massive fillings of small fractures in the host rock.

Geological environment

## Genesis Cancrisilite is a hydrothermal mineral, crystallizing in the late stages of formation of nepheline syenite pegmatites and other ultra-alkaline rocks, rich in sodium and poor in silica. ## Mineral Associations It most often co-occurs with other minerals typical of alkaline massifs, such as nepheline, microcline, sodalite, aegirine, eudialyte, lorenzenite, lamprophyllite, and villiaumite. ## Localities The most important and classic localities of cancrisilite in the world are in Russia, on the Kola Peninsula. These are primarily the ultra-alkaline massifs of Khibiny and Lovozero (e.g., Karnasurt, Koashva, Rasvumchorr mountains).

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp, and undamaged crystals of high transparency. Samples where cancrisilite occurs in association with other rare minerals from the Kola Peninsula, forming aesthetic compositions, also have high value. Crystal size is also an important factor influencing the attractiveness of a specimen. ## Popular Localities The vast majority of the best quality cancrisilite specimens come from pegmatites in the Khibiny and Lovozero massifs on the Kola Peninsula in Russia. These are "type locality" sites for many rare alkaline minerals.

Care and storage

## Cleaning Cancrisilite specimens should only be cleaned with lukewarm distilled water using a very soft brush. Avoid strong rubbing, which could damage the crystal surface or exploit the mineral's perfect cleavage. ## What to Avoid The mineral is sensitive to acids, with which it reacts by releasing carbon dioxide (due to the presence of a carbonate group in its structure). Ultrasonic cleaners, strong detergents, and sudden temperature changes should be avoided. It should not be exposed to prolonged strong sunlight. ## Storage It is recommended to store specimens in separate, sealed boxes or display cases to protect them from dust and mechanical damage. Avoid contact with harder minerals that could scratch its surface.

Sources

IMA Mineral List (CNMNC)