Urphoite
Chemical formula: (U<sup>4+</sup>)<sub>6</sub>(PO<sub>4</sub>)<sub>7</sub>(OH)<sub>3</sub>·4H<sub>2</sub>O
Urphoite is a very rare, secondary uranium mineral of the phosphate group, forming microscopic, yellow crystals.
Properties
- Luster
- Vitreous to greasy
- Streak
- Light yellow
- Density
- 5.13
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification A key diagnostic feature of urphoite is its strong radioactivity, detectable with a Geiger counter. In the field or in a collection, it can be preliminarily identified based on its yellow color, mode of occurrence (small, acicular or tabular crystals in aggregates), and co-occurrence with other secondary uranium minerals. ## Distinguishing from Similar Minerals Urphoite is visually almost impossible to distinguish from many other yellow and greenish-yellow secondary uranium minerals, such as phosphuranylite, uranophane, or autunite, without advanced studies. Definitive identification requires X-ray diffraction (XRD) or chemical analysis (EDS). ## Crystal Forms It forms very fine, elongated crystals with a tabular or bladed habit. These crystals usually occur in small, radial or nearly parallel aggregates, forming crusts on the host rock.
Geological environment
## Genesis Urphoite is a secondary mineral that forms in the oxidation zones of hydrothermal uranium veins. It crystallizes as a result of the slow weathering and alteration of primary uranium minerals, mainly uraninite, in a phosphate-rich environment. ## Mineral Associations It most often occurs in association with other uranium minerals. Its direct mineral associations at the type locality include běhounekite, phosphuranylite, uranophane, gypsum, and remnants of primary uraninite. ## Localities The only confirmed locality of urphoite in the world is its type locality – the Uranus mine in the Annaberg-Buchholz area, in the Ore Mountains (Erzgebirge), Saxony (Germany).
Rarity
Extremely rare
For collectors
## Quality Criteria In the case of a micromineral like urphoite, its collector's value is primarily determined by the richness of the specimen – i.e., the quantity and visibility of aggregates on the rock matrix. Samples with well-formed, distinct microcrystals are highly prized. An additional advantage is an aesthetic combination with other rare associated minerals. ## Popular Localities All known and available urphoite specimens in collections come from a single location in the world: the Uranus mine in Annaberg-Buchholz, Germany. It is therefore a mineral highly valued by collectors specializing in type locality minerals.
Care and storage
## Cleaning Urphoite specimens should generally not be cleaned. They are extremely fragile, and the crystals are easily mechanically damaged. The use of water or chemical agents is not recommended. If necessary, a very soft, dry brush can be used to remove dust, performing this operation with the utmost care. ## What to Avoid Urphoite is a uranium mineral and is radioactive. It is absolutely essential to avoid inhaling dust that might be generated if the specimen is damaged. Hands should be thoroughly washed after any contact with the mineral. It should not be stored in places of permanent human habitation, especially in bedrooms or at desks. It should be protected from mechanical damage and moisture. ## Storage It is recommended to store specimens in sealed, transparent containers (e.g., plastic) that protect against dusting and damage. Each container must be clearly and permanently labeled as radioactive material. It should be kept away from other minerals that may be sensitive to radiation (e.g., smoky quartz, amethyst, topaz) to avoid causing color changes in them.