Phosphuranylite

Chemical formula: KCa(H<sub>3</sub>O)<sub>3</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>7</sub>(PO<sub>4</sub>)<sub>4</sub>O<sub>4</sub>·8H<sub>2</sub>O

Phosphuranylite is a rare, highly radioactive secondary uranium mineral, forming characteristic, bright yellow coatings and crusts on uraniferous rocks.

## Characteristics Phosphuranylite is a hydrated uranyl phosphate of potassium and calcium, belonging to the group of uranium minerals. It most often occurs as microcrystalline aggregates, earthy or powdery coatings, and thin crusts on other minerals. It rarely forms discernible, elongated or tabular crystals, which usually do not exceed fractions of a millimeter and form radial aggregates or rosettes. Its most characteristic feature is its intense, bright yellow to golden yellow color. ## Physical Properties This mineral is very soft, with a hardness of about 2.5 on the Mohs scale. Crystals, when visible, exhibit a vitreous to waxy luster, while earthy aggregates are dull. It is translucent to opaque. Due to its high uranium content, phosphuranylite is a dense mineral, with a specific gravity of about 4.2 g/cm³, and is highly radioactive. Under ultraviolet radiation, it exhibits strong, greenish-yellow fluorescence. ## Colors and Varieties Phosphuranylite occurs in a characteristic palette of yellow shades - from canary yellow, through golden yellow, to yellowish-orange. No named color varieties or commercial names are distinguished. ## History and Name The mineral's name, given in 1879 by Frederick Augustus Genth, directly refers to its chemical composition - it contains phosphates (Phosphor), uranium (Uran), and a hydroxyl group (-yl). It was discovered at the Flat Rock Mine in Mitchell County, North Carolina, USA. ## Uses Due to its rarity and occurrence in small quantities, phosphuranylite has no industrial application. It is of purely scientific and collector's interest, being a subject of interest for specialized collectors of uranium minerals.

Properties

Mohs hardness
2.5
Luster
Vitreous to waxy, dull
Streak
Light yellow
Density
4.2
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features of phosphuranylite are its bright yellow color, occurrence as earthy coatings or microscopic, acicular crystals forming aggregates. Strong radioactivity, measurable with a Geiger counter, is a confirming feature. Intense greenish-yellow fluorescence under UV light is also characteristic. ## Distinguishing from Similar Minerals Phosphuranylite is visually almost impossible to distinguish from many other yellow secondary uranium minerals, such as autunite, meta-autunite, uranophane, or saleeite, without advanced analyses (XRD, EDS). It often co-occurs with them, forming mixtures. In collecting practice, identification is most often based on a label from a reputable source or chemical analysis. ## Crystal Forms Crystals are rare and microscopic, most often in the form of elongated, flattened plates or needles. They usually form radial, stellate, or fan-shaped aggregates, as well as spherulitic clusters and thin coatings on rock surfaces.

Geological environment

## Genesis Phosphuranylite is a secondary mineral, formed in the oxidation (weathering) zones of uranium ore deposits. It forms as a result of phosphate-rich waters acting on primary uranium minerals, such as uraninite. It is a product of alteration under low temperature and pressure conditions, close to the Earth's surface. ## Mineral Associations It most often co-occurs with other secondary uranium minerals, such as uranophane, autunite, torbernite, meta-autunite, as well as primary uraninite. It is also accompanied by quartz, feldspars, micas, and iron oxides (limonite, goethite). ## Localities Key localities worldwide include those in the USA (North Carolina - type locality; Utah; New Hampshire), France (many localities in the Massif Central, including Margnac), Germany (Saxony), Czech Republic (Jáchymov, Příbram), Democratic Republic of Congo (Shinkolobwe), and Australia (Rum Jungle).

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, even microscopic, crystals forming aesthetic, radial aggregates on a contrasting rock matrix. The intensity and purity of the yellow color also increase the specimen's value. Due to the nature of the mineral, crystal size is rarely a key factor - the richness and form of the coating are more important. ## Popular Localities Classic and highly prized specimens come from historical localities in France (e.g., Margnac mine) and from the Ruggles mine in Grafton, New Hampshire, USA, where rich aggregates were found on pegmatites. Specimens from Jáchymov, Czech Republic, also have historical and collector significance.

Care and storage

## Cleaning Phosphuranylite specimens are generally not cleaned. Any attempts at mechanical cleaning (brushes, needles) or chemical cleaning can irreversibly destroy delicate coatings. If absolutely necessary, a stream of compressed air can be used from a safe distance to remove loose dust. ## What to Avoid Contact with water and other liquids, which can dissolve or damage the mineral, must be strictly avoided. It is very soft and brittle, sensitive to any shocks and abrasions. As a highly radioactive mineral, it requires special precautions - direct skin contact, inhalation of dust, and storage in areas of constant human presence should be avoided. ## Storage Specimens should be stored in sealed, lead-lined or thick acrylic containers that limit radiation emission. Containers should be clearly marked with the international radioactivity symbol. Store in a dry place, away from sources of vibration and sunlight, in a well-ventilated room where people do not spend time daily.

External references

Sources

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