Irtyshite

Chemical formula: Na₂Ta₅+₄O₁₁

Irtyshite is an extremely rare tantalum and sodium oxide, forming small, hexagonal crystals with an adamantine luster.

## Characteristics Irtyshite is a rare mineral from the oxide group, chemically classified as sodium tantalate. It forms characteristic, small, tabular or platy crystals with a hexagonal outline. These crystals often occur in clusters, forming rosette-like or granular aggregates. It is a brittle mineral. ## Physical Properties Irtyshite is characterized by significant hardness, measuring 6.5-7 on the Mohs scale, and high density, reaching 7.85 g/cm³. It possesses perfect cleavage in one plane, parallel to the crystal base. Its luster is described as adamantine to resinous, which gives it a distinctive appearance. It is transparent to translucent. ## Colors and Varieties This mineral is most often colorless, white, or whitish-gray. Specimens with a pale, yellowish tint are also found. No named color varieties or commercial varieties are distinguished. ## History and Name The name irtyshite comes from the Irtysh River in eastern Kazakhstan, near which its type locality is situated. The mineral was first described in 1985 by a group of Soviet mineralogists and approved in the same year by the International Mineralogical Association (IMA). ## Applications Due to its extreme rarity, irtyshite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced collections of rare minerals.

Properties

Mohs hardness: 6.5-7
Luster: Adamantine to Resinous
Streak: White
Density: 7.85
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Characteristic features of irtyshite include its hexagonal crystal habit, high density (the specimen is surprisingly heavy for its size), adamantine luster, and perfect cleavage. Its specific occurrence environment in tantalum pegmatites is also crucial for identification. ## Distinguishing from Similar Minerals Irtyshite can be confused with other rare tantalum minerals of similar appearance, such as simpsonite or microlite. From simpsonite, which also crystallizes in the hexagonal system, it differs in chemical composition and slightly different optical properties. Microlite crystallizes in the isometric system, most often forming octahedra. A definitive distinction between these minerals often requires advanced chemical analyses (e.g., EDS). ## Crystal Forms Irtyshite forms thin, tabular crystals with a hexagonal outline. They often intergrow into groups, forming visually attractive rosette-like aggregates. It also occurs as granular aggregates.

Geological environment

## Genesis Irtyshite is a mineral of magmatic origin, crystallizing in the late stages of the evolution of granite pegmatites rich in rare elements, especially tantalum. It forms in zones of intense sodium metasomatism (albitization). ## Mineral Associations This mineral occurs in association with other rare tantalum and niobium minerals, such as tantalite-(Mn), wodginite, simpsonite, and microlite. It also co-occurs with pegmatite-forming minerals like albite, quartz, and muscovite, as well as cassiterite. ## Localities The most important and historical locality for irtyshite is its type locality – the Ungursay mine in the Alakha massif, East Kazakhstan Region, Kazakhstan. It is also known from several other occurrences in tantalum pegmatites, including in the Chinese autonomous region of Xinjiang.

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized irtyshite specimens are those with well-formed, sharp, and undamaged crystals with a hexagonal outline. Aesthetic, rosette-like aggregates are particularly sought after. The transparency and clarity of the crystals, as well as their attractive placement on the rock matrix, especially in association with other rare minerals, are also important. ## Popular Localities The vast majority of the best quality collectible specimens come from the type locality at the Ungursay mine in Kazakhstan. This is the classic and most valued source of this mineral.

Care and storage

## Cleaning Irtyshite specimens should be cleaned very carefully, using a soft brush and distilled water. Due to its perfect cleavage, ultrasonic cleaners should be avoided, as they could cause delamination or cracking of the crystals. ## What to Avoid The mineral is relatively chemically stable, but contact with strong acids and bases should be avoided. It is not sensitive to sunlight or temperature changes under household conditions. It should be protected from impacts and contact with harder minerals that could scratch it. ## Storage It is recommended to store irtyshite specimens in separate, padded display boxes to prevent abrasion and mechanical damage. This also protects other, softer minerals in the collection from potential scratching.

Sources

IMA Mineral List (CNMNC)