Fantappièite

Chemical formula: [Na₈₂.₅Ca₃₃K₁₆.₅]Σ=₁₃₂(Si₉₉Al₉₉O₃₉₆)(S₆+O₄)₃₃·₆H₂O

Fantappièite is a very rare, newly discovered mineral of the cancrinite group, found in Italy, distinguished by its complex chemical composition.

## Characteristics Fantappièite is a mineral with a complex structure and chemical composition, belonging to the cancrinite group. It has been identified as small, anhedral (not exhibiting its own crystallographic forms) grains, with a maximum size reaching 0.5 mm. These grains are colorless and transparent, with a vitreous luster. This mineral is brittle and does not exhibit fluorescence under ultraviolet light. ## Physical Properties Due to its small size and rarity, many physical properties have not been fully determined. Its Mohs hardness is estimated to be around 5. The density calculated based on the chemical formula and unit cell parameters is 2.43 g/cm³. The mineral is characterized by a vitreous luster and is transparent. ## Colors and Varieties So far, only the colorless form of fantappièite has been described. No colored or commercial varieties are known. ## History and Name Fantappièite was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2011 (IMA2011-048). Its name honors Luigi Fantappiè (1901–1956), a distinguished Italian mathematician. The discovery was made on samples from the Pitigliano volcanic complex in Tuscany, Italy. ## Uses Fantappièite has no practical or commercial applications. Its significance is purely scientific and for collectors, as a unique and newly discovered mineral species.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 2.43
Cleavage: None
Fracture: Uneven
Transparency: Transparent
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of fantappièite is impossible without advanced laboratory techniques, such as X-ray diffraction (XRD) and chemical analysis (e.g., electron microprobe). Under collecting conditions, identification relies solely on the label from a confirmed type locality. ## Distinguishing from Similar Minerals Fantappièite is visually indistinguishable from other colorless minerals of the sodalite and cancrinite groups, such as afghanite, liottite, or bystrite, with which it often coexists. Differences can only be determined based on structural and chemical analysis. ## Crystal Forms This mineral forms anhedral, meaning lacking its own faces, grains of irregular shape, up to 0.5 mm in size. No well-formed crystals have been observed.

Geological environment

## Genesis Fantappièite forms under volcanic conditions, in the late stages of magma crystallization. It has been found in porous, phonolitic lavas, as a component of small geodes and rock cavities. Its formation is associated with hydrothermal solution activity within alkali-rich volcanic rocks. ## Mineral Associations This mineral coexists with other rare minerals from the cancrinite and sodalite groups. At the type locality, it was found in association with sanidine, haüyne, liottite, afghanite, bystrite, andradite, and hematite. ## Localities The only confirmed locality for fantappièite in the world is its type locality: Case Collina quarry, located within the Pitigliano volcanic complex, in the province of Grosseto, Tuscany, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, the collector's value of fantappièite primarily depends on confirmed identification and origin from the type locality. The most desirable specimens are those where colorless fantappièite grains are visible (even under a microscope) and contrast with the rock matrix. The presence of rich associations with other rare minerals, such as liottite or afghanite, significantly increases the specimen's value. ## Popular Localities The only source of collector specimens is the type locality – the Case Collina quarry in Pitigliano, Italy. Material from this location is extremely difficult to acquire.

Care and storage

## Cleaning Due to its extreme rarity and fragility, fantappièite specimens, typically in the form of microscopic grains within the host rock, should not be cleaned mechanically or chemically. The safest method is to remove dust using compressed air from a safe distance. ## What to Avoid Avoid contact with all chemicals, acids, and detergents. Do not expose the specimen to ultrasonic cleaners, high temperatures, or sudden temperature changes. Protect from scratches and impacts. ## Storage Specimens should be stored under stable conditions, in a specialized "micromount" box, away from dust, humidity, and direct sunlight. It is best to store them in their original host rock, without attempting to separate individual grains.

Sources

IMA Mineral List (CNMNC)