Nechelyustovite

Chemical formula: (Na&#₉₇₄₄;)&#₉₇₄₄;₂Ba₄Ti₄+₄Nb₅+₄(Na₁₁&#₉₇₄₄;)Ti₄+₄(Si₂O₇)₈O₈(OH)₈(H₂O)₁₂

Nechelyustovite is an extremely rare mineral from the enigmatite group, characterized by an exceptionally complex chemical composition and occurrence as microscopic grains.

## Characteristics Nechelyustovite is an extremely rare mineral with a very complex structure and chemical composition, belonging to the enigmatite group. It occurs as very small, tabular or lath-like crystals, usually not exceeding 0.2 mm in size. Most often, it forms irregular grains or aggregates intergrown with other minerals. Its color is dark brown to almost black, and in transmitted light (in thin fragments), it shows a color ranging from yellowish-brown to reddish-brown. ## Physical Properties The crystals exhibit a luster described as submetallic. The Mohs hardness is 5. The mineral is brittle, and its density, calculated based on the formula and cell parameters, is approximately 3.63 g/cm³. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties This mineral is dark brown to black. Due to its extreme rarity and occurrence as microscopic crystals, no color or commercial varieties are distinguished. ## History and Name Nechelyustovite was discovered in the Khibiny Massif on the Kola Peninsula in Russia. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2006. Its name honors the Russian crystallographer and mineralogist, Dr. Yuri A. Nechelyustov (born 1961), in recognition of his contribution to the study of minerals from the Kola Peninsula. ## Uses Due to its extreme rarity and occurrence only as microscopic crystals, nechelyustovite has no practical or commercial applications. It is solely an object of scientific interest and a valuable acquisition for specialized systematic collections.

Properties

Mohs hardness: 5
Luster: Sub-metallic
Streak: Brown
Density: 3.63
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Triclinic

Diagnostic features

## Identification Identification of nechelyustovite is only possible using advanced laboratory methods, such as chemical analysis (e.g., electron microprobe - EDS/WDS) and X-ray diffraction (XRD). Visually, in the form of microscopic, dark brown to black, tabular crystals with a submetallic luster, it may be suspected in a specific geological environment (agpaitic pegmatites). ## Distinguishing from similar minerals Based on visual characteristics, it is practically impossible to distinguish it from other rare, dark titanium-niobium minerals co-occurring in the same environment, such as enigmatite, astrophyllite, lorenzenite, or lamprophyllite. Definitive differentiation requires specialized analytical studies. ## Crystal forms It forms very small, imperfect crystals with a tabular or lath-like habit, reaching up to 0.2 mm in length. It usually occurs as irregular grains or inclusions in other minerals.

Geological environment

## Genesis Nechelyustovite is a mineral of magmatic origin, crystallizing in the late stages of evolution of highly differentiated, agpaitic alkaline pegmatites. It forms in an environment rich in sodium, barium, titanium, niobium, and silicon, and poor in aluminum. ## Mineral associations This mineral occurs in paragenesis with other rare alkaline minerals. The most common associated minerals include microcline, nepheline, aegirine, lorenzenite, lamprophyllite, eudialyte, as well as other minerals from the enigmatite group, such as jinshajiangite. ## Localities The only confirmed locality (type locality) of nechelyustovite in the world is Mount Nyorkpakhk (Ньоркпахк) in the Khibiny Massif on the Kola Peninsula, Murmansk Oblast, Russia. It occurs there in pegmatites within foyaite.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of a nechelyustovite specimen is assessed quite differently than for more common minerals. The abundance and size of microcrystals on the rock matrix, as well as their association with other rare minerals, are of key importance. A specimen is not evaluated for macroscopic aesthetics, but for its scientific and documentary value. Samples where crystals, despite their microscopic size, are relatively well-formed and identifiable under magnification are most highly prized. ## Popular localities The only source of nechelyustovite specimens is its type locality - Mount Nyorkpakhk in the Khibiny Massif, Russia. All specimens available on the collector's market come from this single location.

Care and storage

## Cleaning Specimens with nechelyustovite, due to the microscopic size of the crystals and their brittleness, should generally not be mechanically cleaned. Any attempts at cleaning may damage or remove the tiny crystals. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. ## What to avoid Avoid contact with any chemicals, ultrasonic cleaners, and sudden temperature changes. The mineral is brittle, so it should be protected from impacts and shocks. ## Storage Specimens should be stored under stable conditions, preferably in their original collector's box (perky box), to protect them from mechanical damage and dust. Identification of the mineral is only possible under a microscope, so it is important to keep a label with precise location and description.

Sources

IMA Mineral List (CNMNC)