Phurcalite

Chemical formula: Ca₂(U⁶⁺O₂)₃O₂(PO₄)₂·7H₂O

Furcalite is a rare, secondary uranium mineral, forming characteristic yellow coatings and aggregates of fine, acicular crystals.

## Characteristics Furcalite is a hydrated uranyl calcium phosphate. It most commonly occurs as aggregates of fine, acicular or bladed crystals, which can form radial aggregates, rosettes, as well as compact or earthy masses and coatings. Individual crystals are usually very small, rarely exceeding 1 mm in length, and often have a bladed habit, elongated in one direction. ## Physical Properties Furcalite crystals exhibit a vitreous to silky luster, and in earthy aggregates, they can be dull. The mineral is translucent. Its Mohs hardness is approximately 2.5, and its density ranges from 3.96 to 4.03 g/cm³. It is strongly radioactive due to its high uranium content. ## Colors and Varieties Furcalite has a characteristic, intense color, from lemon-yellow to golden-yellow. No color or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition - phosphorus (Ph), uranium (ur), and calcium (cal). It was first described in 1978 by P. J. Deliens based on samples from the Shinkolobwe uranium mine in the Democratic Republic of Congo (then Zaire). However, formal approval as a new mineral species occurred only after the discovery and study of better-crystallized specimens from the Ruggles Mine in Grafton, New Hampshire, USA. ## Uses Due to its rarity and small accumulations, furcalite has no industrial application. It is solely an object of interest for collectors specializing in uranium minerals and scientists.

Properties

Mohs hardness
3
Color
Yellow
Luster
Vitreous to silky
Streak
Pale yellow.
Density
4.22
Cleavage
{001} and {010}, perfect. Also {100}.
Fracture
Conchoidal
Transparency
Transparent,Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Furcalite can be identified by its characteristic lemon-yellow color, its form as fine, acicular or bladed crystals forming radial aggregates, and its strong radioactivity. Under shortwave UV light, it exhibits strong, green fluorescence. ## Distinguishing from Similar Minerals Furcalite is visually very similar to many other secondary uranium minerals, such as autunite, meta-autunite, phosphuranylite, or uranophane. It is distinguished from autunite and meta-autunite by the lack of distinct, tabular crystal habit and perfect cleavage. Differentiation from uranophane and phosphuranylite is often impossible without advanced studies (e.g., XRD), although phosphuranylite often forms more compact, earthy aggregates. ## Crystal Forms Crystals are usually very small, acicular or bladed, elongated along the [001] axis and flattened. They form fan-shaped, radial, or stellate aggregates, as well as coatings and efflorescences.

Geological environment

## Genesis Furcalite is a secondary mineral, forming in the oxidation (weathering) zones of uranium deposits. It forms as a result of the alteration of primary uranium minerals, such as uraninite, in the presence of phosphate-rich waters. It is a product of low-temperature hydrothermal processes. ## Mineral Associations It often co-occurs with other secondary uranium minerals, such as phosphuranylite, uranophane, autunite, torbernite, as well as with quartz, muscovite, and clay minerals. ## Localities The most important localities, from which well-formed specimens originate, are the Ruggles Mine in Grafton, New Hampshire (USA) and the locality of Perus, São Paulo (Brazil). It has also been reported from the Shinkolobwe Mine (Democratic Republic of Congo), in Spain (Eureka Mine, Castell-estaó), Germany (Clara Mine, Black Forest), and Australia (Ranger Mine, Northern Territory).

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, large (for this mineral) crystals forming aesthetic, radial aggregates on a contrasting rock matrix. The intensity and purity of the yellow color also increase the value of the specimen. Due to its fragility, specimens undamaged during collection are much more highly valued. ## Popular Localities Specimens from the Ruggles Mine in the USA, which yielded well-defined, bladed crystals, are considered the best in the world. High-quality microcrystals also come from the Clara Mine in Germany.

Care and storage

## Cleaning Furcalite specimens should generally not be wet cleaned. The fine, acicular crystals are extremely fragile and easily damaged. If necessary, compressed air (from a safe distance) can be used to remove dust. Always wash hands after contact with the mineral. ## What to Avoid Avoid contact with water and chemicals. The mineral is fragile and sensitive to mechanical damage. As a uranium mineral, it is strongly radioactive – limit exposure and avoid inhaling dust. ## Storage Furcalite specimens must be stored in sealed, labeled containers, away from areas of constant human presence. It is best to keep them in specialized radioactive mineral display cases. Avoid exposure to direct sunlight, which can cause fading.

External references

Sources

Read more