Bobfinchite

Chemical formula: Na[(U<sup>6+</sup>O<sub>2</sub>)<sub>8</sub>O<sub>3</sub>(OH)<sub>11</sub>]·10H<sub>2</sub>O

An extremely rare, newly discovered uranyl mineral of intense orange color, occurring as microscopic, platy crystals.

## Characteristics Bobfinchite is a newly described, hydrated uranyl sodium oxyhydroxide. It occurs as extremely small, platy or acicular crystals, rarely exceeding 0.2 mm in length. These crystals form radial aggregates or rosettes of intense orange color and vitreous luster. Due to their microscopic size, visual features are difficult to observe without magnification. ## Physical Properties The crystals are too small to reliably determine their hardness or density. The mineral exhibits strong, green fluorescence under short-wave and long-wave ultraviolet light. It is highly radioactive. ## Colors and Varieties This mineral is characterized by a uniform, intense orange color. No varieties have been distinguished. ## History and Name Bobfinchite was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2023 (IMA2023-088). The name honors Robert (Bob) Finch, an American geologist and mineralogist from Argonne National Laboratory, for his significant contributions to uranium mineralogy. ## Uses Bobfinchite has no industrial application. Its significance is purely scientific and collectible, as an extremely rare and newly discovered mineral species.

Properties

Luster
Vitreous
Streak
Orange
Cleavage
Perfect on {010}
Fracture
Brittle
Transparency
Transparent to Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features include its intense orange color, microscopic platy crystal habit forming radial aggregates, and strong green fluorescence under UV light. Final identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Distinguishing from similar minerals It can be confused with other orange-colored secondary uranium minerals, such as becquerelite or curite. Differentiation based on visual characteristics is practically impossible and requires specialized laboratory equipment. Bobfinchite is distinguished by its unique chemical composition and crystal structure. ## Crystal forms It forms elongated, platy or acicular crystals, flattened parallel to {010}. These crystals combine into radial, stellate, or spherical aggregates.

Geological environment

## Genesis Bobfinchite is a secondary uranium mineral, forming in the oxidation zone of uraninite deposits. It crystallizes in voids and fractures as a result of weathering processes of primary uranium ores in the presence of sodium-rich solutions. ## Mineral associations At the type locality (Blue Lizard mine), it is associated with gypsum, calcite, metauranocircite, uranophane, schoepite, and boltwoodite. ## Localities The only confirmed occurrence worldwide is its type locality: Blue Lizard mine, Red Canyon, San Juan County, Utah, USA.

Rarity

Extremely rare

For collectors

## Quality criteria Due to its extreme rarity and microscopic size, any analytically confirmed specimen is valuable. The most highly prized are rich, well-formed, radial aggregates of intense color, contrasting with the rock matrix. The size of the aggregates and the aesthetic appeal of the composition are key factors influencing value. ## Popular localities The only source of specimens is the Blue Lizard mine in Utah, USA. Material from this locality is highly sought after by specialized collectors of rare minerals and micromounts.

Care and storage

## Cleaning Bobfinchite specimens should not be wet cleaned. Dust can only be removed with compressed air or a very soft brush, with utmost care due to the fragility of the crystals and radioactivity. ## What to avoid Contact with water, chemicals, and acids must be strictly avoided. The mineral is sensitive to changes in humidity and temperature. As a uranium mineral, it is highly radioactive – direct contact, dust inhalation, and storage near areas of permanent human presence should be avoided. ## Storage Specimens should be stored in specialized, sealed containers (e.g., micromount type) with appropriate radioactivity labeling. Store in a dry place, away from light and heat sources. It should be isolated from other minerals that could be damaged by radiation.

Sources

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