Natromolybdite
Chemical formula: Na<sub>2</sub>Mo<sup>6+</sup>O<sub>4</sub>·2H<sub>2</sub>O
Natromolybdenite is a rare, hydrated sodium molybdate, most commonly forming colorless or white, acicular crystals and coatings.
Description
## Characteristics Natromolybdenite is a hydrated sodium molybdate, typically occurring as delicate coatings, crusts, and efflorescences. Less commonly, it forms small, well-formed tabular or acicular crystals, which can create radial or tangled aggregates. It is a brittle and delicate mineral. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 2.5. It exhibits a pearly luster on cleavage surfaces and a vitreous luster on other surfaces. It is transparent to translucent. Its density is about 2.36 g/cm³. ## Colors and Varieties Natromolybdenite is most often colorless or white. It can also take on pale yellow or greenish-yellow hues, likely due to the presence of impurities. No named varieties are distinguished. ## History and Name The mineral's name directly refers to its chemical composition – the "natro" component from the Latin *natrium* (sodium) and "molybd" from the element molybdenum. It was first described in 1965 by B.I. Kogan, A.S. Nazarova, and I.M. Isaeva based on material from Kazakhstan. ## Uses Due to its rarity and small accumulations, natromolybdenite has no industrial applications. It is solely an object of scientific and collecting interest.
Diagnostic features
## Identification Characteristic features of natromolybdenite include its occurrence as delicate efflorescences and coatings, low hardness, and water solubility. It often forms directly on molybdenite or in its close vicinity. However, positive identification usually requires advanced analytical methods. ## Distinguishing from Similar Minerals It can be confused with other secondary molybdates, such as powellite or ferrimolybdite. However, powellite is harder and often exhibits fluorescence under UV light, which natromolybdenite does not. Ferrimolybdite is distinguished by its intense yellow color. It can also be confused with other white, soluble sulfates or nitrates that form under similar conditions. ## Crystal Forms It forms small, tabular or acicular crystals, often grouped into radial or chaotic aggregates. It is most commonly found as earthy or fibrous coatings and crusts.
Geological environment
## Genesis Natromolybdenite is a secondary mineral, forming in two main types of environments. Firstly, it forms in the oxidation zones of molybdenum deposits, especially in dry and desert climates, as a weathering product of molybdenite. Secondly, it forms as a sublimation product from volcanic gases in volcanic fumarole exhalations. ## Mineral Associations In the oxidation zones of deposits, it co-occurs with molybdenite, wulfenite, powellite, ferrimolybdite, and gypsum. In volcanic environments, its associations may include other rare molybdates and sulfates formed by sublimation. ## Localities Key localities for this mineral include the Kounrad copper-molybdenum deposit in Kazakhstan (one of the type localities), Kudryavy volcano on the Kuril Islands in Russia, and the Vesuvius fumaroles in Italy. It is also known from several locations in the USA, including the molybdenum deposit in Utah County.
Rarity
Very rare
Collector aspects
## Quality Criteria As a typically microscopic mineral, natromolybdenite is primarily valued by collectors specializing in rare minerals and micromounts. Specimens with well-formed, even if small, crystals, as well as rich coatings on a contrasting matrix, are highly prized. Precisely documented locality is of key importance. ## Popular Localities Specimens from classic fumarolic localities, such as Vesuvius, are most sought after by collectors due to their historical and scientific significance. Specimens from Kazakhstan are also valued as coming from the type locality for this mineral's genesis.
Care and storage
## Cleaning Natromolybdenite is water-soluble, so **it must never be cleaned wet**. The only safe method is gentle dust removal using a soft brush or careful use of a stream of compressed air from a safe distance. ## What to Avoid Avoid all contact with water, water vapor, and other liquids. The mineral is hygroscopic and can be damaged or completely dissolved in a humid environment. It is also very soft and brittle, so it must be protected from impacts, scratching, and abrasion. ## Storage Natromolybdenite specimens require storage in low-humidity conditions. It is best to place them in a sealed, airtight box (e.g., a "membrane box") or in a display case with a desiccant (e.g., silica gel).