Tsaregorodtsevite

Chemical formula: (N(CH₃)₄)₁+Si₄(SiAl)O₁₂

Tsaregorodtsevite is a unique tectosilicate containing a natural tetramethylammonium cation, making it the only known organic mineral with a zeolite structure.

## Characteristics Tsaregorodtsevite is a mineral with an exceptional chemical composition, distinguished by the presence of an organic tetramethylammonium cation in its structure. It belongs to the sodalite group and is the only known example of a mineral with a zeolite structure containing an organic component. It most often forms small, well-formed crystals of a pseudoregular shape, resembling rhombododecahedra or tetrahedra. They are usually colorless, white, or pale yellow and exhibit a vitreous luster. It is an extremely rare mineral, valued mainly by specialized collectors and scientific institutions. ## Physical Properties Tsaregorodtsevite crystals are characterized by a hardness in the range of 6-7 on the Mohs scale, which is similar to quartz. They have a vitreous luster on crystal faces and a greasy luster on fracture surfaces. They are transparent to translucent. The mineral's density is approximately 2.01 g/cm³, making it very light, lighter than most common silicates. ## Colors and Varieties This mineral is most often colorless or white. Specimens with a delicate, pale yellow tint are also found. No named color varieties or commercial varieties are distinguished. ## History and Name Tsaregorodtsevite was discovered in 1991 on Mount Yaruta in the Subpolar Ural Mountains in Russia. Its name honors the Russian mineralogist and collector, Sergey Vasilyevich Tsaregorodtsev (1953-1989), who was an expert on Ural minerals. The mineral was officially approved by the International Mineralogical Association (IMA) in 1993. ## Applications Due to its extreme rarity and small crystal size, tsaregorodtsevite has no industrial applications. Its significance is purely scientific and collectible.

Properties

Mohs hardness: 6-7
Luster: Vitreous, Greasy
Streak: White
Density: 2.01
Cleavage: Poor/Indistinct
Fracture: Uneven to subconchoidal
Transparency: Transparent to Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification A diagnostic feature is its exceptionally low density (approx. 2.01 g/cm³), which makes it unnaturally light to the touch compared to other minerals of similar appearance. The characteristic crystal form, most often pseudoregular, resembling rhombododecahedra, is also distinctive. Under laboratory conditions, chemical analysis showing the presence of nitrogen and methyl groups is the ultimate confirmation. ## Distinguishing from Similar Minerals It can be confused with other colorless or white zeolite minerals or with sodalite. Its very low density primarily distinguishes it from them. Leucite has a similar crystal form but is much denser (approx. 2.5 g/cm³). Analcime also forms similar crystals, but its density is higher (2.22-2.29 g/cm³). ## Crystal Forms Tsaregorodtsevite crystallizes in the orthorhombic system, but its crystals have a pseudoregular (pseudo-isometric) appearance. It most often forms single, well-formed crystals with a shape resembling a rhombododecahedron or tetrahedron, reaching up to 1.5 cm in size. Less frequently, it occurs in granular aggregates.

Geological environment

## Genesis Tsaregorodtsevite forms under hydrothermal conditions in veins cutting through mica schists and quartz-muscovite schists. Its unique composition suggests crystallization from solutions rich in silica, aluminum, and ammonia or organic compounds that were transformed into the tetramethylammonium cation under specific geological conditions. This is an extremely rare process on a global scale. ## Mineral Associations This mineral coexists with quartz, muscovite, rutile, anatase, brookite, hematite, galena, and pyrite. It most often occurs overgrown on quartz crystals or in their company in rock cavities. ## Localities The only confirmed and described occurrence of tsaregorodtsevite in the world is its type locality - Mount Yaruta in the Subpolar Ural Mountains, in the Khanty-Mansi Autonomous Okrug in Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The most valued specimens are those consisting of sharp, well-formed, transparent, and colorless crystals larger than a few millimeters. The crystal form is crucial – the closer to an ideal rhombododecahedron, the more attractive the specimen. Specimens where tsaregorodtsevite crystals are aesthetically set on a matrix, most often on quartz crystals, are also highly rated. Due to its rarity, any well-defined crystal is valuable. ## Popular Localities The only source of collectible specimens is the type locality in the Subpolar Urals in Russia. Material from this location is extremely difficult to obtain, and new finds are practically non-existent, making it one of the rarest minerals on the market.

Care and storage

## Cleaning Specimens should be cleaned only with great care, using a soft brush to remove dust. Compressed air (from a safe distance) may be used. Due to the potential reactivity of the organic cation, contact with water and all chemicals should be avoided. ## What to Avoid Contact with water, acids, bases, and organic solvents must be strictly avoided. The mineral is sensitive to elevated temperatures; heating above 200°C leads to its decomposition and loss of the organic cation. It should be protected from direct sunlight and moisture. ## Storage It is recommended to store specimens in sealed, airtight containers (e.g., "perky box" type) away from heat and moisture sources. It is best to keep them in stable room conditions, in a dark place, to prevent potential degradation.

Sources

IMA Mineral List (CNMNC)