Bonacinaite

Chemical formula: Sc(As₅+O₄)·₂H₂O

Bonacinaite is a hydrated scandium arsenate, a transparent mineral with a vitreous luster, forming small, platy crystals.

## Characteristics Bonacinaite is a hydrated scandium arsenate belonging to the gypsum group. It occurs as very small, thin, platy crystals, typically not exceeding 0.2 mm in length. The crystals are colorless and transparent, with a vitreous luster. ## Physical Properties This mineral is characterized by a hardness of approximately 2 on the Mohs scale, making it very soft. Its density, calculated from crystallographic data, is 2.89 g/cm³. It is a very light mineral. ## History and Name Bonacinaite was discovered in the Brosso quarry in Piedmont, Italy. It was named in honor of Cesare Bonacina (born 1941), an Italian mineral collector and microphotographer, who found the first samples of this mineral. It was approved by the International Mineralogical Association (IMA) in 2022 under the number IMA 2022-031.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: White
Density: 2.89
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of bonacinaite is only possible using advanced analytical methods, such as Raman spectroscopy and X-ray diffraction (XRD), due to the microscopic size of the crystals and their similarity to other secondary minerals. Visually, it is characterized by occurring as small, colorless, platy crystals with a vitreous luster. ## Differentiation from Similar Minerals It can be confused with other arsenates, such as pharmacolite or gypsum, with which it often co-occurs. Differentiation requires chemical analysis confirming the presence of scandium. ## Crystal Forms It forms thin, platy crystals with a lath-like habit, elongated along the [001] axis and flattened parallel to {010}. Crystals are typically very small, with dimensions not exceeding 0.2 mm.

Geological environment

## Genesis Bonacinaite is a secondary mineral that forms as a result of hydrothermal processes in the oxidation zones of ore deposits. At the type locality (Brosso mine), it formed from the oxidation of skutterudite in the presence of scandium-rich solutions, likely originating from the weathering of thortveitite. ## Mineral Associations This mineral co-occurs with other arsenates and secondary minerals. At the type locality, it was found in association with gypsum, kankite, goethite, hematite, quartz, pyrite, and skutterudite. ## Localities The only confirmed occurrence of bonacinaite in the world is the Brosso quarry, located in the municipality of Lessolo, near Ivrea in Piedmont, Italy. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, bonacinaite is not evaluated based on typical macroscopic criteria such as size or color. For collectors of microscopic specimens ("micromounts"), the most important aspects are the quality and abundance of crystals on the rock matrix, their good development, and analytically confirmed identity. The value of a specimen is enhanced by co-occurrence with other rare minerals. ## Popular Localities The only source of specimens is the type locality – the Brosso quarry in Italy. Specimens from this location are highly sought after by specialized collectors of rare minerals.

Care and storage

## Cleaning Due to its extreme rarity and fragility, bonacinaite specimens should only be cleaned by specialists. They typically do not require cleaning as they are stored under special conditions. ## What to Avoid Any contact with water, chemicals, ultrasound, and sudden temperature changes should be avoided. The mineral is very soft (hardness 2), making it extremely susceptible to scratches and mechanical damage. ## Storage Microscopic specimens should be stored in specialized "micromount" boxes, protecting them from dust, vibrations, and light. Any manipulation should be performed using appropriate tools under a microscope.

Sources

IMA Mineral List (CNMNC)