Aldomarinoite

Chemical formula: Sr<sub>2</sub>Mn<sup>3+</sup>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)

Aldomarinoite is a very rare strontium and manganese arsenate, forming characteristic orange-red, tabular crystals.

## Characteristics Aldomarinoite is a hydrated arsenate of strontium and trivalent manganese. It belongs to the bradaczekite group. It forms very small, thin, tabular or bladed crystals, rarely exceeding 0.2 mm. These crystals often arrange themselves into fan-like, rosette-like, or almost spherical aggregates. Due to its size, it is a typical micromount mineral, requiring magnification for observation. ## Physical Properties The crystals exhibit a vitreous, sometimes slightly adamantine luster. They are transparent to translucent. The Mohs hardness is approximately 3. The density calculated from the formula and unit cell parameters is 4.44 g/cm³. ## Colors and Varieties This mineral occurs in a uniform, characteristic orange-red color. The streak is pale orange. No color varieties or commercial varieties are known. ## History and Name Aldomarinoite was recognized as a new mineral by the International Mineralogical Association (IMA) in 2021 (IMA2021-054). Its name honors Aldo Marino (1953–2021), an Italian collector and specialist in minerals from the Aosta Valley region, who first found this mineral. The type locality is the Varenche mine in the Saint-Barthélemy Valley, Italy. ## Uses As a microscopic and extremely rare mineral, aldomarinoite has no commercial or industrial applications. It is solely an object of scientific research and a valuable acquisition for specialized collectors of rare minerals (so-called micromounters).

Properties

Mohs hardness
3
Luster
Vitreous
Streak
Pale orange
Density
4.44
Cleavage
Perfect on {010}
Fracture
Splintery
Transparency
Transparent to Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Key diagnostic features of aldomarinoite include its unique orange-red color, the form of thin, tabular crystals forming rosette aggregates, and its occurrence in a specific geological environment. Due to its microscopic size, definitive identification requires advanced analytical methods, such as Raman spectroscopy or EDS analysis. ## Distinguishing from Similar Minerals It can be confused with other orange or red arsenates, such as erythrite (cobalt-bearing, with a different crystal habit) or some manganese arsenates. Distinguishing based on visual characteristics is very difficult and usually relies on the analysis of associated minerals typical of the given locality. ## Crystal Forms Crystals are thin, tabular, with a bladed or platy habit. They usually occur as radial or spherical aggregates and rosettes, growing on the surface of the host rock.

Geological environment

## Genesis Aldomarinoite is a secondary mineral, formed in the oxidation zone of ore deposits rich in manganese and arsenic. In its type locality (Varenche mine), it forms in fractures within serpentinites containing quartz-carbonate veins. ## Mineral Associations This mineral co-occurs with other rare arsenates and manganese minerals. Its paragenesis includes wallkilldellit-(Mn), brandtite, manganberzeliite, sarkinite, pyrochroite, as well as calcite and quartz. ## Localities The only confirmed locality for aldomarinoite in the world is its type locality – the Varenche mine, Saint-Barthélemy, Nus, Aosta Valley, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of aldomarinoite specimens, which are exclusively micromounts, is assessed based on several criteria. Specimens with sharp, well-formed, and undamaged crystals are most highly valued. The intensity and saturation of the orange-red color are important. Rich, dense aggregates in the form of aesthetic rosettes are more desirable than single, scattered crystals. The value of a specimen is also enhanced by its association with other rare minerals. ## Popular Localities The only source of collector specimens is the Varenche mine in Italy. Material from this locality is extremely limited and primarily goes to specialized collectors and research institutions.

Care and storage

## Cleaning Aldomarinoite specimens are extremely delicate and small. Cleaning should be kept to an absolute minimum. The safest method is to use a soft brush to remove loose dust particles. Due to its chemical composition (arsenate), contact with water should be avoided. ## What to Avoid The mineral is brittle and soft, so it should be protected from impacts and scratches. As an arsenate, it is toxic – avoid inhaling dust and wash hands after each contact. It should not be heated or exposed to chemicals, especially acids, which can damage it. ## Storage It is recommended to store specimens exclusively in specialized micromount boxes, which protect them from mechanical damage and dust. The box should be properly labeled, taking into account the mineral's toxicity.

Sources

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