Eveslogite

Chemical formula: (Ca,K,Na,Sr,Ba)₄₈(Ti₄+,Nb₅+,Fe₂+,Fe₃+,Mn₂+)₁₂(OH)₁₂Si₄₈O₁₄₄(OH,F,Cl)₁₄

Eveslogite is an extremely rare mineral from the cyclosilicate group, forming unique, barrel-shaped crystals with a complex chemical composition.

## Characteristics Eveslogite is a complex cyclosilicate with a very intricate chemical composition, containing calcium, potassium, titanium, niobium, and silicon as main components. It occurs as single, well-formed, barrel-shaped crystals with a hexagonal outline, reaching up to 1 cm in length. The crystals are zonally colored, with a dark brown, almost black core and lighter, yellowish-brown or reddish-brown outer zones. The mineral is brittle. ## Physical Properties The crystals exhibit a hardness of approximately 5 on the Mohs scale. The luster is vitreous to resinous. The mineral is generally opaque, only translucent on thin edges. The measured density is 3.33 g/cm³. ## Colors and Varieties Observed colors include dark brown, reddish-brown, and yellowish-brown, often in the form of zonal distribution within a single crystal. No named varieties have been distinguished. ## History and Name The mineral was approved by the IMA in 2008 (IMA2008-044). Its name comes from its type locality – the Eveslogchorr pegmatite in the Khibiny Massif on the Kola Peninsula in Russia. It was described by a Russian team of mineralogists led by Viktor N. Yakovenchuk. ## Uses Eveslogite has no industrial applications. It is solely an object of scientific and collector interest due to its extreme rarity and unique crystal structure.

Properties

Mohs hardness: 5
Luster: Vitreous to resinous
Streak: Light brown
Density: 3.33
Cleavage: None
Fracture: Uneven
Transparency: Opaque, translucent on edges
Crystal system: Trigonal

Diagnostic features

## Identification The key diagnostic feature is the unique, barrel-shaped form of hexagonal crystals and their characteristic, zonal coloration (dark core, lighter rims). Occurrence in a specific geological environment (agpaitic pegmatites) is also an important clue. Final identification requires advanced analytical methods, such as chemical composition analysis (EDS/WDS) and X-ray diffraction. ## Distinguishing from Similar Minerals Eveslogite may be confused with other rare cyclosilicates from the Kola Peninsula, such as eudialyte or astrophyllite. However, its characteristic barrel-shaped crystal habit distinguishes it, whereas eudialyte typically forms tabular crystals, and astrophyllite forms stellate aggregates. The lack of distinct cleavage differentiates it from minerals of the mica group. ## Crystal Forms It forms single, hexagonal, barrel-shaped crystals, flattened parallel to the basal plane {0001}. The prism faces {10-10} and pyramid faces {10-11} are usually well-developed.

Geological environment

## Genesis Eveslogite forms under hydrothermal conditions in the late stages of crystallization of highly differentiated, alkaline (agpaitic) nepheline syenite pegmatites. It crystallizes in vugs and fissures within these pegmatites. ## Mineral Associations This mineral co-occurs with a number of other rare alkaline minerals. In its type locality, it was found in association with microcline, nepheline, sodalite, aegirine, lorenzenite, lamprophyllite, lomonosovite, eudialyte, sphalerite, galena, and natrolite. ## Localities The only confirmed occurrence of eveslogite in the world is its type locality: pegmatite No. 58 on Mount Eveslogchorr, in the Khibiny Massif, Kola Peninsula, Murmansk Oblast, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly valued specimens are those with sharp, well-formed, undamaged crystals of a distinct, barrel-shaped habit. Desirable features include clear color zoning and a contrasting placement of the crystal on a matrix of other associated minerals (e.g., on white nepheline or microcline). Crystal size is a key factor – specimens exceeding a few millimeters are exceptionally valuable. ## Popular Localities The only source of specimens is the pegmatites of Mount Eveslogchorr in the Khibiny Massif on the Kola Peninsula. Material from this location is extremely limited and rarely appears on the market.

Care and storage

## Cleaning Utmost caution is recommended. Cleaning should be limited to gently removing dust with a soft brush or compressed air from a safe distance. Avoid contact with water and any chemical agents. ## What to Avoid Absolutely avoid ultrasonic cleaners, chemical agents (acids, bases, solvents), and sudden temperature changes. The mineral is brittle and susceptible to mechanical damage. ## Storage Specimens should be stored under stable conditions, in a sealed "micromount" box, protected from dust, moisture, and direct sunlight. Due to its brittleness, avoid vibrations and contact with harder minerals.

External references

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