Ottohahnite
Chemical formula: Na<sub>6</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>5</sub>(H<sub>2</sub>O)<sub>7</sub>·1.5H<sub>2</sub>O
Ottohanite is an extremely rare, radioactive sodium uranyl sulfate, forming microscopic, acicular crystals with intense fluorescence.
Description
## Characteristics Ottohanite is a secondary uranium mineral, occurring as pale yellow or greenish-yellow efflorescences and crusts. It forms extremely small, acicular or prismatic crystals, whose length rarely exceeds 0.1 mm. For this reason, it is classified as a micromount mineral, and its features are only discernible under high magnification. It is transparent and has a vitreous luster. ## Physical Properties Due to the microscopic size and fragility of the crystals, the hardness of ottohanite has not been determined. Its density, calculated based on its chemical formula and crystal structure, is 3.11 g/cm³. A key physical property is its strong, greenish-yellow fluorescence under ultraviolet light (both long- and shortwave), typical of uranyl minerals. ## Colors and Varieties This mineral occurs in a uniform, pale yellow to greenish-yellow color. No color or commercial varieties have been distinguished. ## History and Name The mineral's name honors Otto Hahn (1879–1968), a German chemist and physicist, Nobel laureate, who, together with Fritz Strassmann, discovered the phenomenon of nuclear fission of uranium in 1938. Ottohanite was approved by the International Mineralogical Association (IMA) in 2015, and its full scientific description was published in 2016. It was discovered by Jakub Plášil and his team. ## Uses Ottohanite has no industrial application. Due to its extreme rarity and microscopic size, it is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals (so-called "species collectors").
Diagnostic features
## Identification A diagnostic feature that can be observed without specialized equipment is its very strong, greenish-yellow fluorescence under UV light. In combination with its characteristic occurrence (efflorescences in uranium mines) and pale yellow color, this allows for an initial suspicion of ottohanite's presence. However, final identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS). ## Distinguishing from Similar Minerals Ottohanite can be easily confused with other secondary uranyl sulfates, such as natrozippeite, bluelizardite, or johannite, which often co-occur with it, have a similar color, and also exhibit fluorescence. Visual distinction of these minerals under amateur conditions is practically impossible. They differ in chemical composition and crystal structure, which can only be determined in a laboratory. ## Crystal Forms Ottohanite forms aggregates and efflorescences composed of very fine, acicular or elongated, prismatic crystals. Individual crystals rarely reach 0.1 mm in length and are often intergrown into chaotic aggregates or small, radial groups.
Geological environment
## Genesis Ottohanite is a secondary mineral, formed under specific conditions found in abandoned uranium mine workings. It forms as a product of evaporation of acidic, sulfate-rich mine waters that react with uranium ores. It crystallizes as efflorescences on tunnel walls under conditions of elevated humidity. ## Mineral Associations At its type locality, ottohanite occurs in association with other rare, secondary uranyl sulfates, such as bluelizardite, johannite, and natrozippeite, as well as with gypsum. ## Localities The only confirmed occurrence of ottohanite in the world is its type locality - the Blue Lizard Mine in Red Canyon, San Juan County, Utah, USA.
Rarity
Extremely rare
Collector aspects
## Quality Criteria In the case of a micromount mineral like ottohanite, the value of a specimen is primarily determined by the abundance and quality of the microcrystals. Samples with dense coverage of well-formed, though microscopic, acicular crystals are most desirable. The presence of other rare associated minerals on the same matrix adds additional value. However, the key criterion is certainty of identification, preferably analytically confirmed. ## Popular Localities All known collector specimens come from a single location in the world - the Blue Lizard Mine in Utah, USA. This site is inaccessible to the general public, and material acquisition takes place during specialized research expeditions.
Care and storage
## Cleaning The mineral is water-soluble, so it must absolutely not be cleaned wet. The only permissible method for dust removal is very gentle blowing with air from a safe distance, for example, using a photographic air blower. Any mechanical contact risks destroying the microscopic crystals. ## What to Avoid Avoid contact with water and any chemicals, high humidity, sudden temperature changes, and direct sunlight. As a uranium mineral, ottohanite is radioactive. It should be stored away from light-sensitive materials and other minerals that may be sensitive to radiation. When handling the specimen, basic precautions should be observed: do not inhale dust, do not ingest, and wash hands after contact. ## Storage Ottohanite specimens should be stored under stable conditions, preferably in a tightly sealed, transparent "micromount" box, which protects them from dust, moisture, and mechanical damage. The box should be clearly labeled as containing a radioactive mineral.