Fluorocronite

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

Fluorocronite is a synthetic, colorless lead(II) fluoride, which occurs extremely rarely in nature as microscopic inclusions.

## Characteristics Fluorocronite is a lead(II) fluoride, primarily known as a synthetic compound. Its natural occurrence was confirmed only in 2011 as microscopic, colorless, rounded or irregular grains up to 20 micrometers in size. These inclusions were found within fluorite crystals. Due to its size, the visual characteristics of natural fluorocronite are difficult to observe without specialized equipment. ## Physical Properties As a natural mineral, fluorocronite is too small to determine its physical properties such as hardness or luster. Data primarily comes from its synthetic counterpart. Synthetic fluorocronite has a hardness of 3-4 on the Mohs scale and a density of approximately 7.75 g/cm³. It exhibits a vitreous luster. ## Colors and Varieties Natural fluorocronite is colorless. No varieties are distinguished. ## History and Name The name "fluorocronite" refers to its chemical composition – the dominance of fluorine (fluoro) and lead (cronstedtite, a historical name for lead). The mineral was approved by the International Mineralogical Association (IMA) in 2011 (IMA2011-036). Its discovery was made on material from the uranium ore mine in Okrouhlá Radouň, Czech Republic. ## Uses Natural fluorocronite has no practical applications due to its extreme rarity and microscopic size. Synthetic lead(II) fluoride is used in the production of low-melting-point glasses, infrared-reflecting coatings, and as a scintillating material.

Properties

Mohs hardness: 3-4
Luster: Vitreous
Streak: White
Density: 7.75
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of fluorocronite is impossible without advanced laboratory techniques, such as X-ray microanalysis (EDS/WDS) or electron backscatter diffraction (EBSD). Under collecting or field conditions, it is unrecognizable, as it occurs as microscopic, colorless inclusions in other minerals. ## Distinguishing from Similar Minerals As an inclusion, it can be mistaken for other microscopic mineral inclusions or gas/liquid bubbles. Certain differentiation requires chemical and structural analysis. ## Crystal Forms Natural fluorocronite forms rounded or irregular grains up to 20 micrometers in size. Synthetic lead(II) fluoride crystallizes in the orthorhombic system, forming platy or tabular crystals.

Geological environment

## Genesis Fluorocronite forms in hydrothermal environments. In its type locality (Okrouhlá Radouň, Czech Republic), it was found in fluorite-barite-quartz veins that cut metamorphic rocks. Its formation is associated with the activity of fluorine- and lead-rich solutions at relatively low temperatures. ## Mineral Associations This mineral co-occurs directly with fluorite (in which it forms inclusions), quartz, barite, hematite, uraninite, anglesite, and cerussite. ## Localities The only confirmed natural occurrence of fluorocronite in the world is the Okrouhlá Radouň uranium ore mine, near Jindřichův Hradec in the South Bohemian Region, Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a fluorocronite specimen is entirely dependent on the quality of the host mineral, i.e., fluorite. The collecting appeal of such a specimen is purely scientific and lies in possessing an analytically confirmed, extremely rare mineral. The visual value is negligible, as the inclusions are invisible to the naked eye. ## Popular Localities The only source of natural fluorocronite is its type locality in the Czech Republic. These specimens are practically unavailable on the commercial market and are mainly found in the collections of scientific institutions.

Care and storage

## Cleaning Due to its occurrence exclusively as microscopic inclusions in other minerals (mainly fluorite), fluorocronite specimens themselves are not cleaned. Care applies to the host mineral. Fluorite should be cleaned gently, using a soft brush and distilled water. ## What to Avoid All aggressive chemicals, especially acids, which can damage both fluorocronite and the surrounding fluorite, should be avoided. Sudden temperature changes and ultrasonics, which could cause fractures in the host mineral, should also be avoided. ## Storage Specimens containing fluorocronite inclusions should be stored under stable conditions, away from direct sunlight and heat sources. It is best to store them in padded collector's boxes to protect them from mechanical damage.

Sources

IMA Mineral List (CNMNC)