Dickthomssenite

Chemical formula: MgV⁵⁺₂O₆·₇H₂O

Dickthomssenite is a hydrated magnesium vanadate, forming characteristic golden-brown crystals with a bladed habit.

## Characteristics Dickthomssenite is a hydrated magnesium vanadate, occurring as small but well-formed crystals. Typical specimens consist of aggregates of thin, bladed or acicular crystals, which can form radial or chaotic clusters. Its characteristic features are a golden-brown color and vitreous luster, giving it an attractive appearance despite its small size. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2.5, meaning it can be scratched with a fingernail. It is also very light, with a density of 1.96 g/cm³. The crystals are translucent and exhibit perfect cleavage in one direction, which is visible on some specimens. ## Colors and Varieties Dickthomssenite occurs in a uniform, light golden-brown color. No color varieties or commercial forms are known. ## History and Name The mineral was described in 2001 by William W. Pinch, Howard T. Evans Jr., John E. Taggart Jr., and James A. Hurlbut. Its name honors Richard A. "Dick" Thomssen (b. 1933), an American geologist and mining consultant, for his contributions to the study of uranium and vanadium deposits on the Colorado Plateau. ## Uses Due to its rarity and small crystal size, dickthomssenite has no industrial applications. It is solely a mineral of scientific and collecting interest, sought after by specialists collecting vanadate minerals or microminerals.

Properties

Mohs hardness: 2.5
Luster: Vitreous
Streak: White
Density: 1.96
Cleavage: {100}
Fracture: Hackly
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Dickthomssenite can be identified by its characteristic light golden-brown color, vitreous luster, and form of thin, bladed crystals forming aggregates. It is very soft and light. A white streak is also a helpful feature. ## Distinguishing from Similar Minerals It can be confused with other secondary vanadate minerals, such as carnotite or tyuyamunite, which often co-occur in the same localities. Dickthomssenite differs from them in crystal habit (thin blades instead of tabular crystals), a lighter, golden-brown color (carnotite and tyuyamunite are usually intensely yellow or greenish-yellow), and lack of radioactivity. ## Crystal Forms Crystals are monoclinic, with a bladed or acicular habit, often flattened. They usually form radial aggregates, rosettes, or chaotic clusters on the surface of the host rock, which is most often sandstone.

Geological environment

## Genesis Dickthomssenite is a secondary mineral, forming in the oxidation zone of uranium-vanadium deposits in sandstones. It crystallizes from aqueous solutions in fractures and rock cavities under low-temperature conditions. ## Mineral Associations This mineral co-occurs with other secondary uranium and vanadium minerals, such as carnotite, tyuyamunite, metatyuyamunite, as well as montmorillonite, gypsum, and quartz. ## Localities The most important and type locality for dickthomssenite is the Firefly-Pigmay mine in the La Sal Creek district, San Juan County, Utah, USA. This is the only confirmed locality from which well-documented specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria The most prized dickthomssenite specimens are characterized by rich, dense clusters of well-formed, bladed crystals with an intense, golden-brown color. Contrast with the rock matrix and the absence of damage to the delicate aggregates are also important. Due to the small size of the crystals, specimens are primarily evaluated under magnification. ## Popular Localities The only source of collector specimens is the type locality – the Firefly-Pigmay mine in Utah, USA. All specimens available on the market come from this single location, making them particularly desirable for collectors specializing in rare minerals or minerals from specific localities.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. Due to its low hardness and perfect cleavage, contact with water and mechanical cleaning, even with a soft brush, should be avoided, as this could damage the delicate crystals. ## What to Avoid Avoid contact with all chemicals, including acids and detergents. The mineral is sensitive to changes in temperature and humidity. It should not be heated or exposed to direct sunlight, which can cause dehydration and damage. ## Storage Dickthomssenite specimens, especially those in micromount form, should be stored in closed, stable containers (e.g., "micromount" boxes) to protect them from dust, moisture, and mechanical damage. Display should be in conditions of controlled humidity and away from heat sources.

External references

https://www.mindat.org/min-11216.html