Plavnoite

Chemical formula: K₀.₈Mn²⁺₀.₆[(U⁶⁺O₂)₂O₂(S⁶⁺O₄)]·₃.₅H₂O

Plavnoite is a very rare, secondary uranyl mineral, distinguished by its intense yellow color and occurrence as unique, acicular crystals.

## Characteristics Plavnoite is a hydrated uranyl, potassium, and manganese sulfate. It forms characteristic, prismatic or acicular crystals up to 1 mm long, which often form radial or tangled aggregates. Due to its chemical composition, this mineral is highly radioactive. ## Physical Properties Plavnoite crystals are brittle. The mineral exhibits strong, yellow fluorescence under ultraviolet light (both long-wave and short-wave). Its Mohs hardness is approximately 2, and its calculated density is 4.23 g/cm³. ## Colors and Varieties Plavnoite occurs in an intense yellow color. No varieties have been distinguished. ## History and Name The mineral's name comes from the Plavno mine in the Czech Republic, which is its type locality (the place of its first discovery). It was officially recognized by the International Mineralogical Association (IMA) in 2015 (IMA2015-059). It was described by a team of mineralogists, including Jakub Plášil, a leading researcher of uranyl minerals. ## Applications Plavnoite, due to its extreme rarity and small crystal size, has no industrial applications. It is of purely scientific significance and is a coveted object for specialized collectors of rare and radioactive minerals.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: Light yellow
Density: 4.23
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Characteristic features of plavnoite include its intense yellow color, acicular crystal habit forming radial aggregates, and strong yellow fluorescence under UV light. Its occurrence in association with other secondary uranium minerals in uranium mine dumps is a key indicator. ## Distinguishing from Similar Minerals Plavnoite is visually very similar to many other secondary uranyl sulfates, such as zippeite, johannite, or uranopilite. Definitive differentiation is possible almost exclusively using advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD), which allow for the identification of its unique crystal structure and chemical composition. ## Crystal Forms This mineral forms very fine, acicular or bladed crystals, elongated along the [010] axis. These crystals most often occur as radial, star-shaped, or haphazardly tangled clusters and aggregates.

Geological environment

## Genesis Plavnoite is a secondary mineral, forming in the oxidation (weathering) zone of uraninite deposits. It forms as a result of the activity of sulfate-rich waters reacting with primary uranium ores. Its formation is often associated with post-mining processes in dumps and old mine workings. ## Mineral Associations This mineral co-occurs with other secondary sulfates and uranium minerals. At the type locality (Plavno mine), it was found in association with gypsum, adolfpateraite, johannite, uranopilite, zippeite, and hydrated iron oxides. ## Localities The only confirmed and described occurrence of plavnoite in the world is its type locality – the dumps of the Plavno uranium mine in the Ore Mountains (Krušné hory) in the Czech Republic, near Jáchymov.

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly valued plavnoite specimens are those with well-formed, clearly visible (though still microscopic) crystals forming aesthetic, radial aggregates on a contrasting matrix. Due to their microscopic nature, the quality of photomicrographs is crucial. ## Popular Localities The only source of specimens is the Plavno mine in the Czech Republic. Material from this locality is extremely difficult to obtain and appears on the collector's market sporadically, mainly circulating among specialized collectors of rare minerals (so-called "micromounts").

Care and storage

## Cleaning Plavnoite specimens are generally not cleaned. Any attempts at mechanical or chemical cleaning can irreversibly damage the delicate crystals. Only very careful removal of dust with a soft brush or a photographic air blower is permissible. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and any vibrations or impacts. The crystals are extremely brittle. As a secondary mineral, it is sensitive to changes in humidity and temperature. Due to its uranium content, exposure should be limited, and hands should always be washed after contact with the mineral. ## Storage Plavnoite must be stored under stable conditions, preferably in a sealed, closed "micromount" box, which protects it from mechanical damage and dust. Due to radioactivity, specimens should be kept away from areas of permanent human habitation, in a labeled container, preferably away from other radiation-sensitive minerals.