Ferro-bosiite

Chemical formula: NaFe₃+₃(Al₄Fe₂+₂)(Si₆O₁₈)(BO₃)₃(OH)₃O

Ferro-bosiite is a very rare, black tourmaline group mineral, discovered in Italy and named after mineralogist Ferdinando Bosi.

## Characteristics Ferro-bosiite is a mineral belonging to the tourmaline group. It forms small, prismatic crystals up to 1 mm long, which typically occur in radial aggregates. It is black and opaque, which is typical for many iron-rich tourmalines. ## Physical Properties This mineral is characterized by a hardness of approximately 7 on the Mohs scale and a vitreous luster. Its density is about 3.33 g/cm³. It exhibits no cleavage, and its fracture is uneven to conchoidal. The streak is gray. ## History and Name Ferro-bosiite was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2019 (IMA2019-021). Its name refers to its chemical composition – high iron content (Ferro) – and honors Italian mineralogist Ferdinando Bosi from Sapienza University of Rome for his contributions to the study of the tourmaline group. The mineral was discovered in San Piero in Campo on Elba, Italy.

Properties

Mohs hardness: 7
Luster: Vitreous
Streak: Grey
Density: 3.33
Cleavage: None
Fracture: Uneven to conchoidal
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identification of ferro-bosiite requires advanced analytical methods, such as spectroscopy and chemical analysis (EDS/WDS), due to its visual similarity to other black tourmalines, such as schörl or dravite. In collector conditions, identification relies mainly on the label from a confirmed locality. ## Distinguishing from Similar Minerals It is distinguished from other black tourmalines (e.g., schörl, luinaite-(OH)) by its specific chemical composition, particularly the dominance of Fe³⁺ at the Y site and the simultaneous presence of Fe²⁺ at the Z site of the crystal structure. Visually, it is practically impossible to distinguish. ## Crystal Forms Crystals are prismatic, often terminated by trigonal pyramids. They typically occur as radial or fibrous aggregates.

Geological environment

## Genesis Ferro-bosiite forms in LCT-type (lithium, cesium, tantalum) granite pegmatites. In its type locality (Elba, Italy), it occurs in miarolitic cavities in pegmatites that have undergone late hydrothermal processes. ## Mineral Associations This mineral is associated with quartz, orthoclase, albite, elbaite, schörl, topaz, cassiterite, pollucite, and lepidolite. ## Localities The only confirmed and described locality for ferro-bosiite is its discovery site: the Grotta d'Oggi pegmatite quarry in San Piero in Campo, on the island of Elba, Tuscany, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria As a micromineral, the collector's value of ferro-bosiite primarily depends on the confirmation of its identity through analysis. The most desirable specimens are those with well-formed, even if small, crystals in rock cavities, in association with other pegmatite minerals. Accurate documentation of its origin from the type locality is crucial.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Due to its rarity and the potential fragility of aggregates, avoid washing in water, especially in ultrasonic cleaners. ## What to Avoid Avoid contact with chemicals, acids, and detergents. Do not heat the specimen or expose it to sudden temperature changes. Although tourmalines are relatively hard, protect the mineral from impacts and scratches. ## Storage It is recommended to store specimens in stable conditions, in a closed display box, to protect them from dust and mechanical damage. Avoid exposure to moisture.

Sources

IMA Mineral List (CNMNC)