Tangeite

Chemical formula: CaCu₂+V₅+O₄(OH)

Tangeite is a rare calcium copper hydroxyvanadate, forming characteristic spherical aggregates and coatings of an intense green color.

## Characteristics Tangeite is a mineral from the vanadate group, chemically classified as calcium copper hydroxyvanadate. It most commonly occurs in the form of radial or spherulitic (spherical) aggregates, as well as small, scaly crystals, crusts, and coatings. Individual crystals are usually very small, tabular or bladed, which gives the aggregates a velvety or silky appearance. Its intense, olive-green to emerald-green color makes it easily noticeable against the host rock. ## Physical Properties Tangeite crystals are soft, with a hardness of about 3.5 on the Mohs scale. The mineral is relatively dense, with a specific gravity of approximately 3.89 g/cm³. It exhibits a vitreous to pearly luster, especially visible on fracture surfaces or on the faces of larger crystals. It is usually translucent, rarely transparent in the case of very small crystals. ## Colors and Varieties Tangeite is characterized by a narrow color range. Its color varies from olive-green, through grass-green, to dark, emerald-green. No colored varieties or trade names are known; it is identified solely by its mineralogical name. ## History and Name The mineral was first described in 1925 by Alexander Fersman. Its name comes from its discovery locality – the Tange Gorge in the Alai Mountains, Fergana Valley, Uzbekistan. It is the calcium analog of conichalcite. ## Uses Due to its rarity and occurrence in small aggregates, tangeite has no industrial applications. It is solely an object of interest for mineral collectors, who value it for its intense color and characteristic spherical forms.

Properties

Mohs hardness: 3.5
Luster: Vitreous to Pearly
Streak: Light green
Density: 3.89
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Translucent
Crystal system: Triclinic

Diagnostic features

## Identification Key diagnostic features of tangeite are its forms of occurrence – spherulitic (spherical) or radial aggregates of an intense, olive-green color. A pearly or silky luster on the aggregate surfaces is also characteristic. It reacts with acids, releasing gas bubbles. ## Distinguishing from Similar Minerals Tangeite is sometimes confused with other green secondary minerals, such as malachite, conichalcite, volborthite, or tyrolite. - It differs from **malachite** by its lack of reaction with cold, dilute hydrochloric acid (malachite reacts vigorously) and often a lighter, more olive hue. - It is difficult to distinguish from **conichalcite** visually; this requires advanced chemical analysis (conichalcite contains arsenic, while tangeite contains vanadium). - It differs from **volborthite** in crystal form (volborthite often forms hexagonal tablets) and is often lighter in color. ## Crystal Forms Tangeite forms very small, flattened, tabular or bladed crystals. Most often, they occur as radial aggregates forming spherical clusters (spherulites), fan-shaped rosettes, as well as dense crusts and coatings with a velvety surface.

Geological environment

## Genesis Tangeite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits containing vanadium, copper, and calcium. It forms in dry, arid climatic conditions, as a result of surface water action on primary minerals. It most commonly occurs in fractures and fissures of sandstones, marls, or limestones that contain disseminated copper sulfides and vanadium minerals. ## Mineral Associations This mineral often co-occurs with other secondary copper and vanadium minerals. The most common associations include: conichalcite, volborthite, tyuyamunite, carnotite, malachite, azurite, chrysocolla, as well as calcite and quartz. ## Localities The most important and historical localities of tangeite are in Uzbekistan (Tange Gorge, Alai Mountains). It is also known from numerous localities in the USA, especially in Arizona (e.g., mines in Apache, Coconino, Mohave counties), Utah (e.g., San Juan County), Colorado, and Nevada. Occurrences have also been reported in Germany (Baden-Württemberg, Hesse), England (Cheshire), and the Democratic Republic of Congo.

Rarity

Rare

For collectors

## Quality Criteria The most prized tangeite specimens by collectors are characterized by well-formed, spherical aggregates (spherulites) of an intense, vibrant, olive-green color. Specimens where the spherulites are clearly separated from each other and deposited on a color-contrasting matrix, such as light sandstone, are highly valued. The absence of damage to delicate, velvety surfaces, as well as the size and abundance of occurrences on a single specimen, are also important. ## Popular Localities Although the mineral was discovered in Uzbekistan, specimens from the United States, especially from classic localities in Arizona and Utah, currently dominate the collector's market. Specimens from these locations are valued for their excellent quality and aesthetics.

Care and storage

## Cleaning Tangeite specimens should be cleaned very carefully, preferably using compressed air to remove dust. If necessary, a soft brush can be used. Contact with water, especially hard water or detergents, is not recommended, as it can damage delicate crystals and cause chemical changes on their surface. ## What to Avoid Avoid contact with all chemicals, including acids and bases, which can dissolve the mineral. Tangeite is sensitive to high temperatures and sudden temperature changes. It should not be exposed to prolonged direct sunlight, which can cause fading. It should be protected from moisture. ## Storage Tangeite specimens are best stored in closed, dry containers or display cases to protect them from dust and moisture. Due to its softness and fragility, it should be stored separately, away from harder minerals, to avoid scratches and mechanical damage.

External references

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