Alumino-ottoliniite

Chemical formula: &#₉₇₄₄;NaLi(Mg₃Al₂)Si₈O₂₂(OH)₂

Alumino-ottoliniite is an extremely rare amphibole group mineral, the aluminum analogue of ottoliniite, found in pegmatites on Elba.

## Characteristics Alumino-ottoliniite is a member of the amphibole supergroup, classified as a chain silicate. It forms colorless or pale pink, transparent crystals with a vitreous luster. It occurs as small, prismatic crystals, elongated along one axis, reaching up to 1 mm in length. It is usually found as single, well-formed crystals within small rock cavities, known as miaroles. ## Physical Properties The mineral is characterized by a vitreous luster and is transparent. Its density, calculated based on its chemical composition and unit cell parameters, is approximately 3.05 g/cm³. The Mohs hardness has not yet been determined. ## Colors and Varieties Observed colors are colorless and pale pink. Due to the extreme rarity of the mineral, no varieties have been distinguished. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2016. Its name indicates its chemical composition – it is the aluminum (alumino) analogue of ottoliniite, in which aluminum dominates over magnesium at a specific position in the crystal structure. The name "ottoliniite" honors the Italian chemist Luisa Ottolini for her contribution to the study of amphibole group minerals. ## Applications Alumino-ottoliniite has no industrial applications. As a mineral of primarily scientific importance, it is of interest to specialized collections and research institutions.

Properties

Luster: Vitreous
Streak: White
Density: 3.05
Cleavage: Perfect on {110}
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of alumino-ottoliniite based on visual characteristics is impossible. It requires advanced analytical techniques, such as X-ray microanalysis (EDS/WDS) to determine the precise chemical composition and X-ray diffraction (XRD) to confirm the crystal structure. Key is the determination of aluminum dominance over magnesium in a specific structural position and the presence of lithium. ## Differentiation from Similar Minerals It can be confused with other colorless minerals occurring in the same environment, such as quartz, albite, and especially other amphiboles and tourmalines (elbaite). It is distinguished from the closely related ottoliniite by the dominance of aluminum over magnesium. Definitive differentiation is only possible by laboratory methods. ## Crystal Forms It forms slender, elongated crystals with a prismatic habit. They occur as single, isolated individuals in rock cavities.

Geological environment

## Genesis Alumino-ottoliniite forms in the final stage of crystallization in complex LCT-type (lithium, cesium, and tantalum-rich) granitic pegmatites. It crystallizes within miarolitic cavities from residual, rare-element-rich hydrothermal solutions. ## Mineral Associations This mineral co-occurs with other minerals typical of miarolitic pegmatites, such as quartz, albite, petalite, pollucite, and tourmaline of the elbaite group. ## Localities The only confirmed locality of alumino-ottoliniite in the world is its type locality – the Tres-sorelle pegmatite vein in San Piero in Campo on the island of Elba, Tuscany, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria For microscopic minerals such as alumino-ottoliniite, the value of a specimen is primarily determined by the quality of the crystal itself – its sharpness, lack of damage, and degree of crystal face development. Isolated specimens, set on a contrasting matrix, are desirable. Specimens with a pale pink color may be considered more attractive than colorless ones. A key element of value is the certainty of identification confirmed by analysis. ## Popular Localities The most valuable and only available specimens come from the type locality on the Italian island of Elba. Due to its extreme rarity, this mineral is practically not available on the commercial market and is mainly found in institutional circulation and among specialized collectors.

Care and storage

## Cleaning Alumino-ottoliniite specimens are typically micromounts that do not require cleaning. Any procedures should only be performed by specialists under a microscope, most often using compressed air to remove dust. Contact with water and chemicals should be avoided. ## What to Avoid The mineral is potentially brittle and sensitive to mechanical shocks. It should be protected from contact with any chemicals, acids, and from sudden temperature changes. Ultrasonic cleaning is absolutely forbidden. ## Storage Specimens should be stored in dedicated micromount boxes that protect them from dust, moisture, and mechanical damage. Store in stable room conditions, away from direct sunlight and vibrations.

Sources

IMA Mineral List (CNMNC)