Saccoite

Chemical formula: Ca₂Mn₃+₂F(OH)₈·₀.₅(S₆+O₄)

Saccoite is a very rare mineral from the hydroxyhalide group, forming microscopic, orange-brown, platy crystals.

## Characteristics Saccoite is a hydrated calcium and manganese hydroxyfluoride with an additional sulfate group. It occurs as extremely small, platy or bladed crystals, rarely exceeding 0.2 mm in length. These crystals form rosette-like or radial aggregates, as well as thin coatings and crusts on host rocks. Due to their size, visual features are only discernible under high magnification. ## Physical Properties Saccoite crystals exhibit an orange-brown color and vitreous luster. They are transparent to translucent. Hardness and density have not been precisely measured due to the small size and rarity of the material. The mineral does not show fluorescence under ultraviolet light. ## History and Name The mineral was approved by the IMA in 2017. Its name honors the Italian mineral collector, Franco Sacco (born 1944), in recognition of his contributions to mineralogy, including finding the first samples of the new mineral. It was discovered in the N'Chwaning II mine in South Africa. ## Uses Saccoite has no industrial application. Its significance is purely scientific and collectible, as a unique and newly discovered mineral species.

Properties

Luster: Vitreous
Streak: Pale orange-brown
Cleavage: Perfect on {0001}
Fracture: Micaceous
Transparency: Transparent to translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of saccoite is possible almost exclusively using advanced analytical methods, such as Raman spectroscopy or electron microprobe chemical analysis (EDS/WDS). Visually, in the field or in a collection, identification is impossible. Characteristic (though not unique) features are orange-brown, rosette-like aggregates of microscopic crystals. ## Distinguishing from Similar Minerals It can be confused with other secondary manganese minerals of similar color and habit, such as sturmanite or ettringite, which also occur in the Kalahari mines. Definitive distinction requires specialized laboratory tests. ## Crystal Forms Saccoite forms very small, thin, platy crystals with a hexagonal outline, often elongated and flattened. These crystals combine into radial or rosette-like aggregates, and also form thin coatings.

Geological environment

## Genesis Saccoite is a secondary mineral, formed under low-temperature hydrothermal conditions. It forms in vugs and fractures within manganese ore deposits, likely as a result of alteration of earlier manganese minerals by sulfate- and fluorine-rich solutions. ## Mineral Associations This mineral co-occurs with other rare manganese minerals, such as ettringite, sturmanite, hausmannite, hematite, as well as gypsum and barite. ## Localities The only confirmed locality for saccoite worldwide (type locality) is the N'Chwaning II mine, located in the Kalahari Manganese Field near the town of Kuruman in the Republic of South Africa.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of saccoite specimens is primarily assessed based on the richness and aesthetics of the microscopic aggregates. Most valued are samples with well-formed, distinct crystal rosettes contrasting with the rock matrix. Crystal size, although always microscopic, is also important – larger and better-formed needles are more desirable. Association with other rare minerals is also significant. ## Popular Localities All known collectible specimens come from a single location – the N'Chwaning II mine in South Africa. This is the only source of this mineral on the market.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using compressed air to remove dust. Any contact with water or chemicals is inadvisable due to the microscopic size and fragility of the crystals. ## What to Avoid Avoid contact with all liquids, chemicals, and ultrasound. Specimens are very sensitive to mechanical damage – even touch can destroy delicate crystal aggregates. Protect from high temperatures and humidity. ## Storage It is recommended to store specimens exclusively in specialized, sealed "micromount" boxes, which protect against dust, humidity, and mechanical damage. Display should be away from direct sunlight and sources of vibration.

Sources

IMA Mineral List (CNMNC)