Russellite

Chemical formula: Bi³⁺₂W⁶⁺O₆

Russellite is a rare bismuth tungstate, forming small, yellowish-green crystals and coatings, prized by collectors of rare minerals.

## Characteristics Russellite is a rare mineral from the tungstate group, chemically bismuth tungstate. It most commonly occurs as very small, tabular or pyramidal crystals, which rarely exceed a millimeter in size. It also forms earthy aggregates, powdery coatings, and thin crusts on other minerals. Its characteristic feature is its color, most often in shades from canary yellow to yellowish-green. ## Physical Properties Russellite is a relatively soft mineral, with a hardness of about 3.5 on the Mohs scale. It is distinguished by its very high density, approximately 7.33 g/cm³, which is typical for minerals containing heavy elements such as bismuth and tungsten. It is translucent and exhibits a luster ranging from resinous to adamantine. ## Colors and Varieties This mineral takes on colors from yellow and yellowish-green to creamy and white. No distinct color or commercial varieties are recognized, and its name is the only one used in mineralogy. ## History and Name Russellite was first described in 1938. Its name comes from Sir Arthur Russell (1878–1964), a British mineralogist and prominent mineral collector, who first identified this mineral. The type locality, from which the first studied specimens originated, is the Castle-an-Dinas mine in Cornwall, England. ## Applications Due to its rarity and occurrence in small quantities, russellite has no industrial application. It is of purely scientific and collector's interest, being a sought-after micromount mineral.

Properties

Mohs hardness
3.5
Luster
Resinous to Adamantine
Streak
Pale yellow
Density
7.33
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Russellite is identified by its characteristic yellow to yellowish-green color, high density (the specimen is surprisingly heavy for its size), and mode of occurrence – small tabular crystals or earthy coatings. This often requires analysis under a microscope. ## Distinguishing from Similar Minerals It can be confused with other secondary bismuth and tungsten minerals, such as bismutite, bismite, or stolzite. Bismutite (bismuth carbonate) is usually more creamy or grayish and reacts with hydrochloric acid. Stolzite (lead tungstate) has a similar appearance but often forms larger and better-formed crystals. Definitive differentiation most often requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD). ## Crystal Forms Russellite crystals are typically very small, tabular, with a square or octagonal outline. They also occur in dipyramidal forms. They often form earthy, powdery aggregates or thin coatings.

Geological environment

## Genesis Russellite is a secondary mineral, formed in the oxidation (weathering) zones of ore deposits rich in bismuth and tungsten. It forms as a result of the alteration of primary minerals, such as bismuthinite and wolframite, in the presence of water and oxygen. ## Mineral Associations It often occurs in association with other secondary and primary minerals. The most common associations include: wolframite, scheelite, bismuthinite, bismuth, quartz, fluorite, chalcopyrite, arsenopyrite, as well as other secondary bismuth minerals like bismutite. ## Localities The most important and classic russellite locality is the Castle-an-Dinas mine in Cornwall (England), where it was discovered. Other known localities include the San Nicolás mine in La Rioja (Argentina), the Minas Gerais region in Brazil, as well as individual occurrences in Australia, the Czech Republic, Germany, and the USA (e.g., in Arizona and Nevada).

Rarity

Rare

For collectors

## Quality Criteria For russellite collectors, the quality and size of the crystals are paramount. The most prized specimens are those with well-formed, sharp, lustrous crystals of intense, yellowish-green color, clearly contrasting with the host rock. Due to the microscopic nature of most crystals, their photogenicity under magnification is crucial. The presence of rare associated minerals also enhances the specimen's appeal. ## Popular Localities The most classic and sought-after specimens come from the type locality in Cornwall, England. Specimens from Argentina (San Nicolás mine) have also yielded good quality crystals. Most specimens available on the market are micromounts.

Care and storage

## Cleaning Russellite specimens, especially those in the form of coatings and small crystals, are extremely delicate. They should be cleaned very carefully, preferably using canned compressed air to remove dust. Ultrasonic cleaners, hard brushes, and strong streams of water should be avoided, as they can irreversibly damage the crystals. ## What to Avoid The mineral is sensitive to strong acids. It should be protected from mechanical damage, scratching, and impacts due to its low hardness. It does not require special protection from light or temperature, but extreme conditions should be avoided. ## Storage The best way to store russellite is to place it in a specialized micromount box, which protects delicate crystals from dust and mechanical damage. Display should be in an area away from vibrations and dust.

External references

Sources

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