Belmonteite

Chemical formula: CaMn<sup>2+</sup><sub>2</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub>·H<sub>2</sub>O

Belmonteite is a very rare, hydrated calcium manganese arsenate, forming small, pink, tabular crystals.

## Characteristics Belmonteite is a hydrated calcium manganese arsenate belonging to the roselite group. This mineral forms very small, tabular or bladed crystals, rarely exceeding 0.2 mm in length. These crystals often occur in radial or spherulitic aggregates, as well as in rosette-like clusters. Due to their small size, its visual features are difficult to observe without magnification. ## Physical Properties Belmonteite has a hardness of approximately 3 on the Mohs scale. It exhibits a vitreous to pearly luster, particularly noticeable on cleavage surfaces. It is a transparent to translucent mineral. Its calculated density is approximately 3.33 g/cm³. ## Colors and Varieties This mineral occurs in shades from pale pink to reddish-white. No varieties have been distinguished. ## History and Name Belmonteite was approved as a new mineral by the International Mineralogical Association (IMA) in 2022 (IMA2022-094). Its name comes from its discovery locality – the Belmonte mine in the municipality of Vagli Sotto, Tuscany, Italy. It was described by a team of researchers, including Cristian Biagioni and Luca Brizzi.

Properties

Mohs hardness
3
Luster
Vitreous to pearly
Streak
White
Density
3.33
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of belmonteite is possible almost exclusively through advanced analytical methods, such as Raman spectroscopy or chemical analysis using an electron microprobe (EDS/WDS). Visually, at the occurrence site, it can be suspected based on its pink color, tabular crystal habit, and co-occurrence with other manganese arsenates. ## Distinguishing from Similar Minerals Belmonteite is very similar to other minerals of the roselite group, especially roselite itself (a cobalt-rich variety) and brandtite (a manganese-rich variety). Distinguishing these minerals requires precise chemical analysis to determine the dominant element in a given structural position. ## Crystal Forms Crystals are very small, with a tabular or bladed habit, flattened parallel to the {010} plane. They form radial, spherulitic, or rosette-like aggregates.

Geological environment

## Genesis Belmonteite forms as a result of hydrothermal processes in quartz-barite veins cutting through manganese-rich rocks. It is a secondary mineral, crystallizing in the late stage of deposit formation. ## Mineral Associations This mineral co-occurs with barite, quartz, brandtite, kutnohorite, pyrochroite, sarkinite, and other unidentified manganese arsenates. ## Localities The only confirmed occurrence of belmonteite worldwide is its type locality – the Belmonte mine, located in the municipality of Vagli Sotto, in the Province of Lucca, Tuscany, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" mineral of scientific value, the most important criterion is the certainty of specimen identification. Visual appeal is enhanced by well-formed, undisturbed crystal aggregates with intense pink coloration, contrasting with associated minerals (matrix). Any specimen with confirmed analysis is extremely valuable. ## Popular Localities The only source of specimens is the Belmonte mine in Italy, making it a key locality for collectors specializing in rare minerals or minerals from specific locations.

Care and storage

## Cleaning Due to its extreme rarity, small size, and fragility, belmonteite specimens should not be cleaned mechanically or chemically. Any impurities are best left intact to avoid damaging the brittle crystals. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and sudden temperature changes. As an arsenate, it is potentially toxic, and inhalation of dust and direct skin contact should be avoided. ## Storage Specimens should be stored exclusively in specialized, sealed "micromount" containers, protecting them from dust, vibrations, and mechanical damage. Store in a dry place, away from sunlight.

Sources

Read more