Carnotite
Chemical formula: K<sub>2</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(V<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>·3H<sub>2</sub>O
Carnotite is a bright yellow, highly radioactive uranium and vanadium mineral, occurring mainly as coatings and powdery aggregates on sedimentary rocks.
Description
## Characteristics Carnotite is a hydrated potassium uranyl vanadate, known primarily for its intense, canary-yellow color. It rarely forms crystals visible to the naked eye, most often occurring as powdery or earthy coatings, aggregates, and impregnations in sedimentary rocks, mainly sandstones. It can also form crusts or fill small fractures. Due to its habit, specimens are usually dull and opaque, although very fine crystals may exhibit a weak luster. ## Physical Properties It is a very soft mineral, with a hardness of only 2 on the Mohs scale, meaning it can be scratched with a fingernail. It has a dull, earthy luster, and in denser aggregates, it can be waxy or weakly pearly. It is translucent in very thin splinters, but in aggregate form, it is completely opaque. Its density is approximately 4.95-5.05 g/cm³, making it relatively heavy for a mineral with a non-metallic appearance. ## Colors and Varieties It is characterized by a constant, diagnostic color in shades from bright yellow, canary yellow, to slightly greenish-yellow. It does not form color varieties or commercial varieties – its name is unequivocally linked to its composition and appearance. ## History and Name The name carnotite, given in 1899 by French scientists Charles Friedel and Éphrem-Louis-Clément Cumenge, honors Marie Adolphe Carnot (1839–1920), a French chemist and mining engineer who first identified this mineral in samples from Colorado. ## Uses Carnotite is one of the most important uranium ore minerals, as well as a significant source of vanadium. Its large-scale exploitation, especially in the first half of the 20th century on the Colorado Plateau in the USA, was crucial for the development of nuclear programs and as an alloying additive to steel (vanadium).
Diagnostic features
## Identification The key diagnostic feature of carnotite is its intense, canary-yellow color combined with a powdery or earthy habit. The most important test, however, is radioactivity measurement – carnotite exhibits strong activity, easily detectable with a Geiger counter. It usually does not fluoresce under ultraviolet light. ## Distinguishing from Similar Minerals Carnotite is very similar to tyuyamunite (its calcium analogue). Distinguishing them without chemical analysis is almost impossible. Tyuyamunite, however, more often exhibits weak, greenish-yellow fluorescence in UV. Other yellow secondary uranium minerals, such as autunite or torbernite, usually have better-formed, tabular crystals and fluoresce strongly (autunite green). It is distinguished from native sulfur by its much higher density and radioactivity. ## Crystal Forms Well-formed crystals are extremely rare and appear as small, lath-like or tabular forms with monoclinic symmetry. The vast majority of the material consists of microcrystalline aggregates, powdery aggregates, coatings, and impregnations of the matrix rock (mainly sandstone).
Geological environment
## Genesis Carnotite is a secondary mineral, formed in the oxidation zone of uranium and vanadium deposits. It forms under desert or semi-desert conditions as a result of groundwater action, which leaches and concentrates these elements in porous sedimentary rocks, such as sandstones and conglomerates. It often precipitates on organic matter, such as silicified wood or dinosaur bones, which act as a reducing environment. ## Mineral Associations It most often co-occurs with its calcium analogue, tyuyamunite. It is also accompanied by other secondary uranium and vanadium minerals, such as metatorbernite, rossite, hewettite, as well as clay minerals, calcite, and gypsum. Its occurrence in association with silicified wood is characteristic. ## Localities The most important and historical carnotite deposits are located on the Colorado Plateau in the USA (states of Utah, Colorado, Arizona, New Mexico), from which classic specimens originate. Significant occurrences are also known from Kazakhstan, Australia (Radium Hill), the Democratic Republic of Congo, Gabon, and Morocco.
Rarity
Not very common
Collector aspects
## Quality Criteria The most prized carnotite specimens are characterized by an intense, bright yellow color and rich coverage of the matrix rock. Samples in which carnotite forms impregnation or crusts on silicified wood or fossil vertebrate bones are particularly sought after. Due to the dusty nature of the mineral, specimens that form compact, rather than loose, aggregates are more highly valued. ## Popular Localities The historical mines of the Uravan district in Montrose County (Colorado, USA) and the Grants area (New Mexico, USA) are considered classic and provide the best specimens. Specimens from these localities, especially on fragments of fossilized wood, are the standard for this mineral.
Care and storage
## Cleaning Carnotite specimens are generally not cleaned. It is a very soft, brittle, and often dusty mineral. Any attempt at wet cleaning can damage it or wash it off the matrix rock. If necessary, dust can be very carefully removed with a soft brush, performing this action outdoors or in a well-ventilated area, using a dust mask. ## What to Avoid Carnotite is **highly radioactive**. Inhaling dust and ingesting its particles should be strictly avoided. Contact with the mineral should be kept to a minimum. After each touch of the specimen, hands should be thoroughly washed. It should not be stored in bedrooms, workplaces, or other rooms where a lot of time is spent. Radiation can damage other minerals (e.g., blacken smoky quartz, destroy the color of fluorite), so it should be kept away from the rest of the collection. ## Storage Carnotite specimens should be stored in sealed, transparent containers (e.g., plastic) that prevent the spread of dust and the accumulation of radon – a gaseous product of uranium decay. The container must be clearly labeled as radioactive material. It is best to keep it in a well-ventilated area, away from people and animals.