Amgaite

Chemical formula: Tl₃+₂Te₆+O₆

Amgait is an extremely rare copper and thallium arsenate, forming microscopic, green crystals with a strong luster.

## Characteristics Amgait is a very rare mineral from the arsenate group, containing thallium and copper. It occurs as very small, prismatic or acicular crystals, rarely exceeding 0.2 mm in length. These crystals often form radial or fan-shaped aggregates. A characteristic feature of the mineral is its intense green color and very strong, almost adamantine luster. ## Physical Properties Amgait's luster is adamantine, and the mineral is translucent. Its density, calculated based on chemical composition and unit cell parameters, is approximately 5.8 g/cm³. Hardness on the Mohs scale has not yet been determined due to the very small size of the crystals. ## Colors and Varieties Amgait occurs exclusively in green of varying saturation. No color varieties or commercial forms are known. ## History and Name The mineral was officially described in 2017. Its name comes from the Amga River in Yakutia (Russia), the home region of one of the authors of the mineral's description, N.V. Krivolutskaya. Interestingly, the name is not related to the discovery site, which is the Vorontsovskoe gold deposit in the Urals, Russia. ## Applications Due to its extreme rarity, microscopic size, and toxic chemical composition (thallium and arsenic content), amgait has no practical applications. It serves solely as an object of scientific research and interest for specialized micromineral collectors.

Properties

Luster: Adamantine
Streak: Light green
Density: 5.8
Transparency: Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of amgait is possible almost exclusively using advanced analytical methods, such as energy-dispersive spectroscopy (EDS) or X-ray diffraction (XRD), which can confirm its unique chemical composition. Preliminary diagnostic features include green color, adamantine luster, acicular crystal habit in radial aggregates, and specific occurrence. ## Distinguishing from Similar Minerals Amgait can be confused with other secondary green arsenate minerals, such as olivenite, conichalcite, or euchroite. The key distinguishing feature, only ascertainable analytically, is the presence of thallium in its composition, which is not found in the aforementioned minerals. ## Crystal Forms The mineral forms elongated, prismatic to acicular crystals. Most often, they occur as small, radial or fan-shaped aggregates, as well as disordered clusters on the surface of the host rock.

Geological environment

## Genesis Amgait is a secondary mineral that forms in the oxidation (weathering) zone of ore deposits. It originated from hydrothermal processes acting on primary sulfide ores rich in arsenic and thallium. ## Mineral Associations At the only known locality, amgait co-occurs with other rare thallium and arsenic-bearing minerals, such as vorontsovite and chursinite, as well as with quartz and native gold. ## Localities The only confirmed locality of amgait in the world is the Vorontsovskoe gold deposit in the Sverdlovsk Oblast, Ural region, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of collector specimens of amgait, which are exclusively microminerals, is assessed based on the sharpness and size of the crystals, as well as the aesthetics of their arrangement within the aggregate. Specimens where amgait forms well-defined, radial clusters on a contrasting host rock background are highly valued. Co-occurrence with other rare minerals from the same locality also increases its value. ## Popular Localities The only specimens that have ever appeared in collections come from the type locality – the Vorontsovskoe gold deposit in the Urals, Russia.

Care and storage

## Cleaning Cleaning amgait specimens is strongly discouraged. Due to its toxicity and fragility, any attempts at cleaning can lead to damage to the delicate crystals and contamination of the environment. Cleaning should be left exclusively to experts under laboratory conditions. ## What to Avoid Avoid all skin contact and inhalation of dust that might be generated when handling the specimen. Amgait contains thallium and arsenic – two highly toxic elements. Do not heat the mineral or expose it to acids. Store away from moisture. ## Storage Amgait specimens must be stored in tightly sealed, clearly labeled containers (e.g., "perky box" type) to prevent accidental contact and dust dispersion. It should be kept away from other minerals to avoid potential chemical interaction.

Sources

IMA Mineral List (CNMNC)