Feklichevite

Chemical formula: Na₁₁Ca₉(Fe³⁺,Fe²⁺)₂Zr⁴⁺₃Nb⁵⁺(Si₂₅O₇₃)(OH,H₂O,Cl,O)₅

Feklichevite is a rare, dark brown mineral from the eudialyte group, distinguished by its complex chemical composition containing zirconium and niobium.

## Characteristics Feklichevite is a complex cyclosilicate belonging to the eudialyte group. It typically forms granular aggregates or imperfectly developed, tabular crystals with a hexagonal outline. Its characteristic feature is a dark brown color. It is a translucent mineral with a vitreous luster. ## Physical Properties This mineral has a hardness of 5.5 on the Mohs scale. Its density is 2.87 g/cm³. It exhibits perfect cleavage in one plane, and its fracture is uneven, sometimes stepped. The streak, which is the color of the powdered mineral, is brownish. ## Colors and Varieties Feklichevite occurs in a uniform, dark brown color. No color or commercial varieties have been distinguished. ## History and Name The mineral is named in honor of Mikhail Feklichev (1931–1999), a Russian mineralogist and crystallographer who made significant contributions to the study of minerals from the eudialyte group. Feklichevite was approved as a new mineral species by the International Mineralogical Association (IMA) in 2000. The type locality from which this mineral was first described is the Kovdor phlogopite mine in the Kovdor Massif, Russia. ## Uses Feklichevite has no industrial applications. Its significance is limited to the scientific and collecting spheres, as a rare and well-defined representative of the eudialyte group.

Properties

Mohs hardness: 5.5
Luster: Vitreous.
Streak: Brownish
Density: 2.87
Cleavage: Perfect on {0001}.
Fracture: Irregular/Uneven,Step-Like
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Feklichevite can be identified by its dark brown color, vitreous luster, and tabular crystal habit. Its perfect cleavage in one direction is also characteristic. Its occurrence in a specific geological environment (alkaline massifs) is an important diagnostic clue. ## Distinguishing from Similar Minerals Feklichevite is very similar to other minerals from the eudialyte group, such as eudialyte itself or manganoeudialyte. Distinguishing it from them based on visual features is practically impossible and requires advanced analytical methods, such as chemical analysis (EDS/WDS) or X-ray diffraction (XRD), to confirm the dominance of iron, zirconium, and niobium in specific structural positions. ## Crystal Forms Feklichevite crystals are usually poorly formed, having a tabular habit and a hexagonal outline. It most often occurs as disordered grains or granular aggregates within the host rock.

Geological environment

## Genesis Feklichevite is a mineral of magmatic origin. It forms in the late stages of crystallization within ultra-alkaline, silica-saturated intrusions, such as nepheline syenites and associated pegmatites. ## Mineral Associations This mineral co-occurs with other minerals typical of alkaline massifs. In the type locality (Kovdor), it was found in association with calcite, cancrinite, pectolite, phlogopite, apatite, titanite, pyrochlore, zircon, and other minerals from the eudialyte group. ## Localities The most important and well-documented occurrence of feklichevite is its type locality – the Kovdor phlogopite mine in the Kovdor Massif, on the Kola Peninsula in Russia. This is the only confirmed locality from which well-studied specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria The most valuable specimens for collectors are those with well-formed, sharp-edged crystals of distinct tabular habit and an intense, dark brown color. Rich aggregates of crystals in a contrasting rock matrix, especially in association with other rare minerals, are also highly prized. Purity and absence of mechanical damage significantly increase the value of a specimen. ## Popular Localities The only source of collectible feklichevite specimens is the Kovdor Massif in Russia. Specimens from this locality are considered reference material for this species.

Care and storage

## Cleaning Feklichevite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, a damp cloth with distilled water can be used, and the specimen should then be immediately dried. Ultrasonic cleaners should be avoided. ## What to Avoid This mineral is sensitive to strong acids and other chemicals. It should be protected from sudden temperature changes and prolonged exposure to direct sunlight, which can affect its appearance. Due to its perfect cleavage, it is susceptible to mechanical damage. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratches and impacts. Stable environmental conditions should be maintained, away from sources of moisture and chemical contaminants.