Baumoite

Chemical formula: Ba<sub>0.5</sub>[(U<sup>6+</sup>O<sub>2</sub>)<sub>3</sub>O<sub>8</sub>Mo<sup>6+</sup><sub>2</sub>(OH)<sub>3</sub>](H<sub>2</sub>O)<sub>3</sub>

Baumoite is an extremely rare uranyl and molybdenum mineral, forming microscopic, yellow platy crystals.

## Characteristics Baumoite is a very rare, complex oxide of uranyl, barium, and molybdenum. It occurs as extremely small, platy crystals with a hexagonal outline, reaching sizes up to 20 micrometers. These crystals form rosette-like or spherical aggregates. Due to their microscopic size, visual characteristics are difficult to observe without specialized equipment. ## Physical Properties Baumoite crystals exhibit a yellow luster. Hardness and density have not been determined due to the small amount of available material. The mineral shows strong, green fluorescence under shortwave ultraviolet light (254 nm). ## Colors and Varieties Baumoite is a mineral of uniform, yellow color. No varieties have been distinguished. ## History and Name The mineral is named in honor of Werner Baum (born 1940), a German mineral collector from Schlema, Saxony, who found the first sample. Baumoite was approved as a new mineral species by the International Mineralogical Association (IMA) in 2022 (IMA2022-044). It was described by Jakub Plášil and his research team. ## Uses Baumoite has no industrial application. As an extremely rare microscopic mineral, it is of purely scientific significance and is of interest to specialized collectors of uranium minerals (so-called "micromounts").

Properties

Luster
Vitreous
Streak
Yellow
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of baumoite is possible only through advanced analytical methods, such as X-ray diffraction (XRD) and chemical spectroscopy (EDS), due to its microscopic size and occurrence. Preliminary indications may include its yellow color, platy crystal habit, and strong green fluorescence under UV light; however, these features are common to many secondary uranium minerals. ## Distinguishing from Similar Minerals Baumoite is visually almost impossible to distinguish from other secondary, yellow uranyl minerals, such as uranophane, boltwoodite, or other uranyl molybdates (e.g., iriginite, calcurmolite) without specialized examination. Chemical analysis confirming the presence of barium, uranium, and molybdenum in specific proportions is crucial. ## Crystal Forms It forms very thin, platy crystals with a hexagonal outline, which often combine into rosette-like or spherical aggregates.

Geological environment

## Genesis Baumoite is a secondary mineral formed in the oxidation (weathering) zone of uranium-molybdenum deposits. It forms as a result of groundwater interaction with primary uranium ores (uraninite) and molybdenum in the presence of barium. ## Mineral Associations At the type locality (Svornost mine), baumoite is associated with uraninite, hematite, quartz, calcite, fluorite, gypsum, and other rare uranyl molybdates, such as calcurmolite and wulfenite. ## Localities The only confirmed locality of baumoite in the world is its type locality: the Svornost mine in Jáchymov, Karlovy Vary Region, Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the quality of a specimen is primarily determined by the abundance and good development of crystals visible under magnification. Rosette-like aggregates with distinct, sharp, undamaged crystal edges, set on a contrasting matrix, are most highly valued. ## Popular Localities The only known and most highly valued specimens come from the Svornost mine in Jáchymov, Czech Republic.

Care and storage

## Cleaning Baumoite specimens should not be cleaned mechanically or chemically. Any attempts at cleaning may irreversibly destroy the microscopic crystals. They should be protected from dust. ## What to Avoid As a uranium mineral, baumoite is radioactive and should be handled with appropriate precautions. Direct contact, inhalation of dust, and storage in areas of permanent human presence should be avoided. It should be protected from moisture, chemicals, and high temperatures. ## Storage Specimens should be stored in sealed, lead-lined, or appropriately shielded containers, away from other radiation-sensitive minerals. The container should be clearly labeled as radioactive material. It is best stored in specialized "micromount" boxes.

Sources

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