Metatamboite

Chemical formula: Fe<sup>3+</sup><sub>3</sub>(OH)(H<sub>2</sub>O)<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)(Te<sup>4+</sup>O<sub>3</sub>)<sub>3</sub>(Te<sup>4+</sup>O(OH)<sub>2</sub>)(H<sub>2</sub>O)

Metatamboite is an extremely rare, secondary iron tellurate-sulfate, forming earthy coatings in the oxidation zones of gold deposits.

## Characteristics Metatamboite is a secondary mineral, formed by the dehydration of tamboite. It occurs as earthy, dusty, or powdery coatings and aggregates on the surface of the host rock. It does not form macroscopic, well-developed crystals. Its aggregates are usually very fine-grained and have a dull, lusterless appearance. ## Physical Properties Due to its mode of occurrence, many physical properties of metatamboite are difficult to determine precisely. The luster is typically earthy or dull. The mineral is opaque. The density calculated from the chemical formula and unit cell parameters is approximately 4.65 g/cm³, but there are no measured data. Hardness has not been determined. ## Colors and Varieties Metatamboite is characterized by a yellowish-brown to brown color. No color or commercial varieties have been distinguished. ## History and Name The mineral's name refers to its association with tamboite and its discovery locality. The prefix "meta-" indicates its origin through transformation (dehydration) of tamboite. The second part of the name comes from the Tambo mine in the El Indio-Tambo district (Coquimbo, Chile), where it was first identified. The mineral was officially approved by the International Mineralogical Association (IMA) in 2012. ## Uses Metatamboite, as an extremely rare mineral occurring in small quantities, has no industrial application. It is solely an object of scientific interest and is valued by specialized collectors of rare minerals.

Properties

Luster
Earthy
Streak
Light yellow
Density
4.65 (obliczona)
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Amateur identification of metatamboite is practically impossible. Its appearance – yellowish-brown, earthy coatings – is non-specific and can resemble many other secondary iron minerals, such as jarosite or goethite. A key clue is its geological environment (oxidation zone of tellurium deposits) and co-occurrence with other tellurates. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Metatamboite is visually indistinguishable from many other earthy, yellow, and brown secondary minerals. It can be confused with tamboite (from which it forms), jarosite, as well as other rare iron tellurates and tellurites. Final differentiation relies solely on laboratory analysis of its chemical composition and crystal structure. ## Crystal Forms Metatamboite does not form crystals visible to the naked eye. It occurs exclusively as very fine-grained, earthy, or powdery aggregates, forming thin coatings and efflorescences.

Geological environment

## Genesis Metatamboite is a secondary mineral. It forms in the oxidation zones of hydrothermal gold and tellurium deposits. It is created directly as a result of the natural dehydration process of the mineral tamboite, under dry, weathering conditions. ## Mineral Associations This mineral occurs in direct proximity to the mineral from which it forms – tamboite. It is also accompanied by other secondary tellurium minerals, such as emmonsite and mackayite, as well as quartz and native gold. ## Localities The only confirmed and described locality of metatamboite worldwide is its type locality – the Tambo mine, located in the El Indio-Tambo district in the Coquimbo region, Chile.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, metatamboite is evaluated by collectors according to specific criteria. The most important is the abundance and richness of the coating on the host rock. Specimens where metatamboite occurs in association with other rare, well-identified tellurium minerals are highly valued. Confirmation of diagnosis by analysis is crucial for the scientific and collector's value of the specimen. ## Popular Localities For collectors, the only source of metatamboite is its type locality in Chile. Specimens from this mine are extremely rare on the collector's market.

Care and storage

## Cleaning Metatamboite specimens are extremely delicate and susceptible to mechanical damage. Cleaning should be kept to an absolute minimum. Only very careful removal of dust with a stream of compressed air from a distance is permissible. Any physical contact should be avoided. ## What to Avoid This mineral cannot be wet-cleaned, using water, or any chemical agents. Ultrasonic cleaners, which would destroy the fragile, earthy aggregates, must be absolutely avoided. It should be protected from shocks, vibrations, and abrasion. ## Storage It is recommended to store specimens exclusively in closed "micromount" boxes, which protect them from dust and mechanical damage. They should be kept in a dry place with a stable temperature, away from sources of vibration.

Sources

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