Barahonaite-(Al)

Chemical formula: (Ca,Cu₂+,Na,Fe₃+,Al)₁₂Al₂(As₅+O₄)₈(OH,Cl)x·nH₂O

Barahonaite-(Al) is a very rare, hydrated arsenate, forming characteristic spherical aggregates of a light blue color.

## Characteristics Barahonaite-(Al) is a secondary, hydrated arsenate belonging to the arsenate group. It occurs as crusts and aggregates with a botryoidal or spherulitic structure, reaching several centimeters in diameter. Its most characteristic feature is its vivid, light blue, sky-blue, or blue-green color. It is an amorphous mineral, meaning it does not form regular crystals. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2-3. It has a vitreous, waxy, and sometimes dull luster. It is translucent to opaque. Its density ranges from 3.0-3.1 g/cm³. Due to its amorphous nature, it does not exhibit cleavage, and its fracture is uneven or conchoidal. ## Colors and Varieties The predominant color is light blue, often described as sky-blue. It can also take on blue-green hues. Barahonaite-(Al) is the aluminum (aluminous) analogue of Barahonaite-(Fe), in which iron dominates the same structural position. Both minerals form a series but differ in color – the iron variety is usually green. ## History and Name The mineral is named in honor of Antonio Barahona (born 1938), a Spanish mineral collector and dealer who found the first specimens. It was officially recognized by the International Mineralogical Association (IMA) in 2006. The suffix "-(Al)" distinguishes it from its iron counterpart, Barahonaite-(Fe), according to mineral nomenclature rules. The type locality is the La Profunda mine in Asturias, Spain. ## Applications Barahonaite-(Al) has no industrial applications. Its significance is purely scientific and collectible due to its rarity, attractive appearance, and association with a specific locality.

Properties

Mohs hardness: 2-3
Luster: Vitreous to Waxy, Dull
Streak: Light blue
Density: 3.0-3.1
Cleavage: None
Fracture: Uneven to Conchoidal
Transparency: Translucent to Opaque

Diagnostic features

## Identification Key diagnostic features include its habit (spherical or reniform aggregates), characteristic light blue color, low hardness, and paragenesis with other secondary copper arsenates. Vitreous to waxy luster and a light blue streak are also helpful in identification. ## Distinguishing from Similar Minerals Barahonaite-(Al) can be confused with chrysocolla, which has a similar color and form but is a silicate and often has a slightly different, more "glassy" appearance. It can also be confused with turquoise, which is, however, much harder (5-6 on the Mohs scale). Final differentiation from other rare blue arsenates, such as agardite, requires advanced chemical analysis (e.g., EDS). ## Crystal Forms As an amorphous substance, Barahonaite-(Al) does not form well-developed crystals. It occurs exclusively as botryoidal, spherulitic, mammillary aggregates, and as thin crusts and coatings.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation (weathering) zones of polymetallic ore deposits rich in arsenic and copper. It forms as a result of the alteration of primary arsenic minerals, mainly arsenopyrite, in an aluminum-rich environment. ## Mineral Associations It most commonly co-occurs with other secondary arsenate minerals, such as olivenite, conichalcite, scorodite, pharmacosiderite, and mansfieldite. It is also accompanied by iron oxides and hydroxides (goethite) and sulfates (jarosite, gypsum). ## Localities The most important and practically sole source of well-formed collector specimens is the type locality – the La Profunda mine, Villaviciosa de Asturias in Asturias, Spain. Occurrences in other parts of the world have not yet been unequivocally confirmed.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens are characterized by an intense, uniform, light blue color and well-formed, spherical aggregates with a distinct luster. The size of the aggregates and their aesthetic placement on a contrasting rock matrix are also of great importance. Specimens with visible associations of other rare minerals, especially crystalline ones, are particularly sought after. ## Popular Localities All significant collector specimens come from a single location in the world: the La Profunda mine in Asturias (Spain). This makes it a highly desirable mineral for collectors specializing in systematics or minerals from specific localities.

Care and storage

## Cleaning Specimens should only be dry-cleaned using a soft brush to remove dust. Contact with water, especially hot water, is not recommended, as it is a hydrated mineral and may undergo changes. If absolutely necessary, distilled water can be used, but contact should be as brief as possible, and the specimen should be dried immediately. ## What to Avoid Avoid all chemical agents, acids, and detergents. The mineral is soft and brittle, so it must be protected from impacts and scratches. Do not heat it or use ultrasonic cleaners, which could damage its delicate structure. ## Storage It is recommended to store specimens in separate, padded boxes to prevent abrasion. Protect it from moisture, direct sunlight, and extreme temperatures. Stable room conditions are most suitable.

Sources

IMA Mineral List (CNMNC)