Braccoite

Chemical formula: NaMn²⁺₅[Si₅O₁₄(OH)](As⁵⁺O₃OH)

Braccoite is a very rare, orange-brown sodium manganese arsenosilicate, forming small, platy crystals.

## Characteristics Braccoite is a sodium manganese arsenosilicate with a complex chemical composition. It occurs as very small, platy or lamellar crystals, usually not exceeding 0.3 mm. It forms rosette-like or spherulitic aggregates. Its characteristic feature is an intense, orange-brown color. ## Physical Properties Braccoite crystals exhibit a vitreous luster. This mineral is transparent to translucent. Due to the small size of the crystals, precise determination of hardness and density is difficult; the density calculated from the formula and cell parameters is approximately 3.61 g/cm³. ## Colors and Varieties Braccoite occurs in a uniform, orange-brown color. No varieties have been distinguished. ## History and Name The mineral was discovered in the Valgraveglia manganese ore mine in Liguria, Italy. It was approved by the International Mineralogical Association (IMA) in 2013 under number 2013-088. The name honors Pierfranco Bracco (born 1959), an Italian mineral and micromount collector who found the first samples of this mineral. ## Uses Braccoite has no industrial application. It is solely an object of scientific interest and for advanced collectors specializing in rare minerals and micromounts.

Properties

Color
Brown-red
Luster
Vitreous
Streak
Pale yellow
Density
3.56
Cleavage
Perfect on {001}
Fracture
Irregular/Uneven
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Braccoite is recognizable by its unique appearance: orange-brown, platy or lamellar crystals forming rosette-like aggregates. However, identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS), due to its rarity and small crystal size. ## Distinguishing from Similar Minerals It can be confused with other rare manganese arsenosilicates from the same locality, such as tiragalloite or palenzonaite. Definitive differentiation is possible only through detailed crystallochemical studies. ## Crystal Forms Crystals are very small, thin, and platy, often with a hexagonal outline. They intergrow into characteristic, rosette-like or spherulitic aggregates.

Geological environment

## Genesis Braccoite forms as a result of metamorphic processes in manganese ore deposits that have been subjected to hydrothermal activity. It occurs in calcite veins cutting rocks rich in braunite and quartz (radiolarites). ## Mineral Associations This mineral coexists with calcite, braunite, quartz, ganophyllite, saneroite, axinite, and tiragalloite. ## Localities The only confirmed occurrence of braccoite in the world is its type locality – the Valgraveglia mine, located in the municipality of Ne in Liguria, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria The most valued specimens are those with well-formed, distinct rosettes or crystal aggregates, contrasting with the rock matrix (most often calcite). Due to the microscopic nature of the mineral, the size of the aggregates and the intensity of the color are key factors influencing its attractiveness. ## Popular Localities The only source of braccoite specimens is the Valgraveglia mine in Italy, which is its type locality. All specimens available on the collector's market come from this single location.

Care and storage

## Cleaning Braccoite specimens, typically micromounts, do not require cleaning. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Avoid ultrasonic cleaners, chemical agents, acids, and high temperatures. Fragile crystals are very susceptible to mechanical damage. ## Storage It is recommended to store specimens only in specialized micromount boxes to protect them from dust, moisture, and physical damage. Display should only be done under a microscope.

External references

Sources

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