Andymcdonaldite

Chemical formula: Fe₃+₂Te₆+O₆

Andymcdonaldite is an extremely rare iron tellurate, forming microscopic, hexagonal crystals of an intense red-orange color.

## Characteristics Andymcdonaldite is an iron tellurate with the formula Fe₂TeO₆. It occurs as very small, hexagonal, prismatic crystals, rarely exceeding 0.1 mm in size. It most often forms small, granular aggregates or single, scattered crystals on the surface of the host rock. Its most characteristic features are its intense red-orange to brownish-red color and strong luster. ## Physical Properties This mineral is characterized by a adamantine luster. It is translucent to transparent. Its density, calculated based on chemical composition and crystal structure, is 5.61 g/cm³. The Mohs hardness has not yet been determined. ## Colors and Varieties Andymcdonaldite occurs in shades from bright red-orange to deeper, brownish-red. No color varieties or commercial varieties have been distinguished. ## History and Name The mineral was named in honor of Dr. Andrew M. McDonald (born 1961), a Canadian mineralogist from Laurentian University, in recognition of his contributions to the study of tellurium mineralogy. The mineral was officially approved by the International Mineralogical Association (IMA) in 2017. It was discovered in the Aga mine in Shizuoka Prefecture, Japan. ## Applications Due to its extreme rarity and microscopic size, andymcdonaldite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized micromineral collectors.

Properties

Luster: Adamantine
Streak: Light yellow
Density: 5.61
Cleavage: None
Transparency: Translucent to transparent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of andymcdonaldite under amateur conditions is practically impossible. Preliminary identification is based on microscopic observation of characteristic, hexagonal crystals with a red-orange color and adamantine luster. A key indicator is its occurrence in association with other rare tellurates in the only known locality. ## Differentiation from Similar Minerals It can be confused with other intensely colored, secondary tellurium minerals that may coexist with it. Definitive differentiation from minerals such as mcalpineite or kuranakhite requires advanced analytical methods, such as energy-dispersive spectroscopy (EDS) or X-ray diffraction (XRD), which allow for precise determination of chemical composition and crystal structure. ## Crystal Forms Andymcdonaldite crystallizes in the form of short, hexagonal prisms, often terminated by flat pinacoid faces. It occurs as single, well-formed microcrystals or as small, granular aggregates.

Geological environment

## Genesis Andymcdonaldite is a secondary mineral, formed in the oxidation zone of low-sulfide, epithermal ore veins rich in gold and tellurium. It forms as a result of weathering and alteration of primary tellurides under near-surface conditions. ## Mineral Associations This mineral occurs in association with native gold, quartz, as well as other rare tellurates and tellurium oxides, such as mcalpineite, kuranakhite, and several other as yet unnamed mineral phases. ## Localities The only confirmed occurrence of andymcdonaldite in the world is the Aga mine (Aga Au-Ag-Te deposit) in Goshiki, Shizuoka Prefecture on Honshu Island, Japan. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria In the case of a micromineral like andymcdonaldite, the collector's value is primarily determined by the quality and development of the crystals. Specimens with sharp, undamaged, hexagonal crystals of intense color and strong luster are most prized. Rich mineralization, meaning a large number of crystals on a small area of the host rock, as well as aesthetic associations with other rare minerals, are also highly valued. ## Popular Localities All known specimens of andymcdonaldite come from a single location – the Aga mine in Japan. Material from this locality is extremely difficult to acquire and appears on the collector's market sporadically, mainly going to specialized micromineral collectors.

Care and storage

## Cleaning Andymcdonaldite specimens, due to their rarity and small crystal size, require extreme caution. Cleaning should be limited to gently removing dust with compressed air from a safe distance. Any contact with water or chemical agents is discouraged. ## What to Avoid Ultrasonic cleaners, all acids, solvents, and detergents must be absolutely avoided. The crystals are fragile and susceptible to mechanical damage, so the specimen should be protected from impacts, vibrations, and friction. Its resistance to light and temperature is unknown, so it is recommended to avoid exposure to direct sunlight and sudden thermal changes. ## Storage The safest storage method is to place the specimen in a sealed "micromount" box, which protects against dust, moisture, and mechanical damage. Display should be in stable environmental conditions.

Sources

IMA Mineral List (CNMNC)