Napoliite

Chemical formula: Pb<sup>2+</sup><sub>2</sub>OFCl

Napoliite is a rare lead oxychloride fluoride, forming colorless, prismatic crystals in the fumaroles of Mount Vesuvius, Italy.

## Characteristics Napoliite is a lead oxychloride fluoride. It forms small, colorless to white, prismatic crystals, rarely exceeding 0.2 mm in length. These crystals often occur as aggregates, arranged in parallel or forming divergent groups. ## Physical Properties The mineral is characterized by a adamantine luster and is transparent. Its density, calculated from the chemical formula and unit cell parameters, is 7.18 g/cm³. Hardness has not yet been determined. ## Colors and Varieties Napoliite is colorless to white. No varieties have been distinguished. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2022 (IMA2022-060). Its name comes from the city of Naples (Italian: Napoli), near which Mount Vesuvius is located – the only known locality of this mineral. ## Applications Due to its extreme rarity and microscopic crystal size, napoliite is of purely scientific and collectible interest.

Properties

Luster
Adamantine
Streak
White
Density
7.18
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of napoliite requires advanced research methods, such as X-ray diffraction (XRD) or chemical spectroscopy (EDS). Preliminary visual identification is based on observing colorless, prismatic crystals with an adamantine luster in samples from Vesuvius fumaroles. ## Distinguishing from Similar Minerals It can be confused with other colorless lead halides found in the same environment, such as cotunnite (PbCl₂), laurionite (PbCl(OH)), or paralaurionite (PbCl(OH)). Definitive differentiation is only possible through chemical and crystallographic analysis, as napoliite is the only one of these that contains fluorine. ## Crystal Forms It forms elongated, prismatic crystals, often terminated by flat faces. It occurs as single crystals or aggregates with parallel or radial structures.

Geological environment

## Genesis Napoliite forms by sublimation from volcanic gases in high-temperature fumaroles (at temperatures of approximately 500-600°C). It is a product of the reaction of gases rich in lead, chlorine, fluorine, and oxygen. ## Mineral Associations It co-occurs with other fumarolic minerals, mainly lead halides, such as cotunnite, laurionite, paralaurionite, and challacolloite. ## Localities The only confirmed locality in the world is its type locality – the La Fossa crater on Mount Vesuvius, in the province of Naples, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria Specimens with well-formed, transparent crystals, clearly separated from the matrix, are most highly valued. Association with other rare minerals from this locality adds additional value. ## Market Prices Reliable market data is unavailable due to extreme rarity and recent discovery. Specimens appear sporadically in the offerings of specialized rare mineral dealers. ## Popular Localities All known specimens come from a single location – the fumaroles on Mount Vesuvius in Italy.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to their microscopic size and potential reactivity, contact with water and other liquids should be avoided. ## What to Avoid Avoid contact with chemicals, acids, and water. As a lead mineral, it is toxic – avoid inhaling dust and wash hands after any contact. Store away from moisture. ## Storage The safest storage method is a sealed, transparent "micromount" box, protecting delicate crystals from mechanical damage, dust, and moisture.

Sources

Read more