Rietveldite
Chemical formula: Fe<sup>2+</sup>(U<sup>6+</sup>O<sub>2</sub>)(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>5</sub>
Rietveldite is an extremely rare, secondary uranyl iron sulfate, forming brittle, yellow coatings and aggregates in uranium mines.
Description
## Characteristics Rietveldite is a mineral belonging to the sulfate group, chemically a hydrated iron uranyl sulfate. It occurs as delicate, brittle coatings and crusts of efflorescence. It forms aggregates of small, platy or fibrous crystals, which rarely reach sizes visible to the naked eye. Its most characteristic feature is an intense, lemon-yellow to greenish-yellow color. ## Physical Properties This mineral is very soft, with a Mohs hardness of about 2. It is extremely brittle and delicate. The luster is described as vitreous on crystal surfaces or silky in the case of fibrous aggregates. It is translucent. Its density, calculated based on chemical composition and structure, is approximately 3.65 g/cm³, but it cannot be measured in a traditional way due to its mode of occurrence. ## Colors and Varieties Rietveldite occurs in uniform shades, from light yellow and lemon to greenish-yellow. No color or commercial varieties are distinguished. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2016. Its name honors the Dutch crystallographer Hugo M. Rietveld (1932–2016), creator of the Rietveld method, a fundamental technique used in powder diffraction data analysis to refine crystal structures. The discovery was made on material from the Blue Lizard Mine in San Juan County, Utah, USA, which is its type locality. ## Applications Due to its extreme rarity, small size, and instability, rietveldite has no industrial application. It is solely an object of scientific interest and a prized acquisition for specialized collectors of rare minerals and uranium minerals.
Diagnostic features
## Identification Features that allow identification of rietveldite include its characteristic lemon-yellow color, its occurrence as delicate coatings and efflorescences, and its geological environment – oxidation zones of uranium deposits, often on the walls of old mine workings. A key diagnostic feature is strong, green fluorescence under ultraviolet light (both shortwave and longwave). However, final confirmation of identity requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Rietveldite can be easily confused with many other yellow secondary uranium minerals, such as zippeite, johannite, uranophane, or meta-autunite. Distinguishing them based on visual characteristics is usually impossible. Rietveldite is distinguished by its specific chemical composition (presence of iron) and unique crystal structure, which can only be determined under laboratory conditions. ## Crystal Forms It forms microscopic, elongated crystals with a platy or acicular habit. They usually occur as tangled aggregates, fibrous aggregates, and coatings and crusts covering the host rock.
Geological environment
## Genesis Rietveldite is a secondary mineral. It forms under supergene conditions, i.e., near the Earth's surface, as a result of weathering processes. It forms as a product of the oxidation of primary uranium minerals (mainly uraninite) and sulfides (pyrite) under the influence of waters containing dissolved oxygen. It is a typical mineral of the oxidation zone of uranium deposits, often crystallizing as efflorescences on the walls and faces of mine workings in dry climates. ## Mineral Associations It co-occurs with other secondary sulfates and uranium minerals. Its most common associated minerals are gypsum, halotrichite, hexahydrite, römerite, as well as the primary minerals from which it forms – uraninite and pyrite. ## Localities This is an extremely rare mineral, known from only a few localities worldwide. The type locality, from which the best and most numerous specimens originate, is the Blue Lizard Mine in Red Canyon, San Juan County, Utah, USA. In addition, its presence has been noted in the Schlema-Alberoda uranium deposit in Saxony (Germany).
Rarity
Extremely rare
Collector aspects
## Quality Criteria The quality of rietveldite specimens is primarily assessed based on the richness and surface coverage of the host rock by the mineral. Samples with intensely colored, dense crystalline aggregates are most valued. An additional advantage is the presence of other rare associated minerals on the same specimen. Due to the microscopic size of the crystals, their individual form is not a key evaluation criterion. ## Popular Localities Virtually all specimens available on the collector's market come from a single locality – the Blue Lizard Mine in Utah, USA. This is the classic and most important locality for this mineral.
Care and storage
## Cleaning The mineral is extremely delicate and water-soluble. **Absolutely no wet cleaning is allowed.** Any attempt at mechanical cleaning, even with a soft brush, risks irreversible damage to the specimen. It is recommended to leave it in an untouched state. ## What to Avoid - **Water and moisture:** Contact with water leads to the dissolution of the mineral. Avoid storing in a humid environment. - **Dry air and heat:** As a hydrated mineral, rietveldite is sensitive to dehydration. Storage in too dry or warm a place can cause the loss of water from its structure, leading to disintegration and alteration into another mineral. - **Mechanical damage:** It is very soft and brittle. Avoid touching, shocks, and any pressure. - **Radiation:** Rietveldite is a radioactive mineral. Limit direct contact, wash hands after each touch, and do not store specimens in places of permanent residence (desk, bedroom). ## Storage The best way to store it is to place the specimen in a tightly sealed, transparent container (such as a "membrane box" or a box with a seal). This will protect it from mechanical damage and stabilize the ambient humidity, protecting the mineral from dehydration. The container must be clearly labeled as containing a radioactive mineral.