Arangasite

Chemical formula: Al<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)(PO<sub>4</sub>)F·9H<sub>2</sub>O

Arangaite is a very rare, hydrated aluminum fluorophosphate-sulfate, forming tiny, bluish-green aggregates and crusts.

## Characteristics Arangaite is a very rare secondary mineral from the phosphate and sulfate group. It occurs as microscopic, bladed crystals, most often forming rosette aggregates, spherulites, or thin crusts on rock surfaces. Its small size makes individual crystals difficult to observe with the naked eye, and material for study is extremely limited. ## Physical Properties Arangaite crystals exhibit a vitreous luster. Due to the microscopic size of the crystals, many physical properties, such as hardness, density, or fracture, have not been precisely determined. The mineral is transparent to translucent. ## Colors and Varieties Arangaite is characterized by a pale, bluish-green color. No color varieties or commercial varieties are known. ## History and Name The mineral was discovered in the Aranga granite mine in the municipality of Aracuai, Minas Gerais state, Brazil. Its name comes directly from its type locality. It was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 2011 under number 2011-039. The first scientific description was published in 2012 by a team of researchers, including Daniel Atencio. ## Applications Arangaite, due to its extreme rarity and microscopic size, has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals (so-called micromounts).

Properties

Mohs hardness
2
Luster
Vitreous
Streak
White
Density
2.16
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Amateur identification of arangaite is practically impossible. This mineral is recognized by its characteristic form – tiny, bladed crystals forming rosette aggregates – and its pale bluish-green color. Its specific occurrence environment is also crucial. Final confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical spectroscopy (EDS). ## Differentiation from Similar Minerals Arangaite can be confused with other secondary phosphate and sulfate minerals of similar appearance and color, such as wavellite, turquoise, or some minerals from the chalcosiderite group. Distinguishing it from these minerals requires specialized research equipment. The geological context (co-occurrence with specific minerals in granite vugs) is an important clue. ## Crystal Forms Arangaite crystallizes as very small, bladed or tabular crystals, elongated along one axis. These crystals almost always occur in the form of radial or rosette aggregates and spherulites, as well as thin coatings and crusts on the surface of the host rock.

Geological environment

## Genesis Arangaite is a secondary mineral that forms as a result of hydrothermal processes occurring in the late stage of granite pegmatite crystallization. It forms in small cavities and fissures (miarolitic cavities) in granite, crystallizing from solutions rich in aluminum, phosphorus, sulfur, and fluorine. ## Mineral Associations This mineral occurs in association with other minerals typical of granite pegmatites. In its type locality, its co-occurrence with albite, quartz, muscovite, fluorite, as well as rarer minerals such as zanazziite, eosphorite, wardite, strengite, and variscite has been noted. ## Localities The only confirmed locality of arangaite in the world is its type locality – the Aranga granite mine (also known as Córrego da Laje) in the municipality of Aracuai, in the Jequitinhonha Valley, Minas Gerais state, Brazil.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of arangaite specimens is primarily assessed based on the richness and aesthetics of the crusts. Specimens showing well-formed, though microscopic, rosette aggregates of intense, bluish-green color are most valued. Contrast with the rock matrix and the absence of damage to the delicate crystals are also important. Due to the microscopic nature of the mineral, the size of individual crystals is not a key criterion; rather, the overall area covered by the mineral is more important. ## Popular Localities The only source of arangaite specimens is the Aranga mine in Minas Gerais, Brazil. Material from this locality is extremely rare and sought after by collectors specializing in systematic minerals and micromounts.

Care and storage

## Cleaning Arangaite specimens, usually microscopic crusts on the host rock, are extremely delicate. Cleaning should be kept to an absolute minimum. If necessary, compressed air (from a safe distance) can be used to remove loose dust particles. Any contact with water or brushes should be avoided. ## What to Avoid Contact with water, chemicals, acids, and detergents, which can damage or dissolve this delicate mineral, must be strictly avoided. It should not be subjected to ultrasonic cleaning. Specimens should be protected from high temperatures and direct sunlight, which can lead to dehydration and loss of color. ## Storage It is recommended to store arangaite specimens exclusively in specialized micromount boxes that protect them from dust, moisture, and mechanical damage. Display should be in stable environmental conditions, away from sources of vibration and contamination.

Sources

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