Virgilluethite

Chemical formula: Mo<sup>6+</sup>O<sub>3</sub>·H<sub>2</sub>O

Virgilluethite is a hydrated molybdenum(VI) oxide, being the mineralogical analogue of synthetic molybdenum trioxide trihydrate (α-Molybdic Acid).

## Characteristics Virgilluethite is a hydrated molybdenum(VI) oxide, approved as a new mineral by the IMA in 2023. It occurs as very small, platy crystals up to 20x5x1 micrometers, forming aggregates and coatings. It is the mineralogical analogue of synthetic molybdenum trioxide trihydrate, known as α-Molybdic Acid. ## Physical Properties Due to the microscopic size of the crystals, most physical properties, such as hardness, density, or luster, have not been precisely determined. The crystals are flexible. ## Colors and Varieties The mineral is colorless to white. No varieties have been distinguished. ## History and Name The mineral is named in honor of Virgil W. Lueth (born 1958), retired director of the New Mexico Bureau of Geology and Mineral Resources, in recognition of his contributions to mineralogy and economic geology, particularly in New Mexico. The mineral was discovered on the dumps of the Questa mine in New Mexico, USA, and its description was published in 2024. ## Uses Virgilluethite has no industrial applications. It is of purely scientific and collector's interest as a very rare mineral.

Properties

Luster
Vitreous
Streak
White
Cleavage
Perfect on {010}
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of virgilluethite is only possible using advanced analytical methods, such as Raman spectroscopy and X-ray diffraction (XRD). Visually, it is unrecognizable due to its microscopic size and uncharacteristic appearance (white coatings). ## Distinguishing from Similar Minerals It can be confused with other secondary molybdenum minerals, such as molybdite (MoO₃) or kelyanite. Molybdite is anhydrous and has a different crystal structure. Distinguishing it from other rare, hydrated molybdenum oxides requires specialized equipment. ## Crystal Forms It forms microscopic, lath-like or platy crystals, elongated along the [001] axis and flattened parallel to {010}. These crystals aggregate into small, rosette-like or tangled clusters and thin coatings on the surface of the host rock.

Geological environment

## Genesis Virgilluethite is a secondary mineral that forms as a result of the weathering (oxidation) of molybdenite (MoS₂) under low-temperature and high-humidity conditions. It forms in an acidic environment, on mine dumps and in the oxidation zones of molybdenum deposits. ## Mineral Associations It co-occurs with molybdenite, pyrite, quartz, gypsum, and other secondary molybdates and sulfates. ## Localities The only confirmed worldwide occurrence (type locality) is the dumps of the Questa molybdenum mine in Taos County, New Mexico, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the value of a specimen is primarily determined by the richness and abundance of coatings on the rock matrix. The best specimens are those where virgilluethite is clearly visible (though still microscopic) and well-formed, and its identity has been analytically confirmed. Association with other minerals is also important. ## Popular Localities The only source of specimens is the Questa mine in New Mexico, USA. Material from this locality is extremely rare on the collector's market.

Care and storage

## Cleaning Due to extreme delicacy and reactivity, virgilluethite specimens should not be cleaned mechanically or chemically. They should be treated solely as exhibits for observation. ## What to Avoid Avoid contact with water, chemicals, and any attempts at ultrasonic cleaning. The mineral is sensitive to changes in humidity and temperature, which can lead to its dehydration and disintegration. It should be protected from dust and touch. ## Storage Specimens should be stored under stable conditions, preferably in closed, airtight containers (so-called micromount boxes), to minimize the impact of changes in air humidity. Store in the dark, away from heat sources.

Sources

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