Daubréeite

Chemical formula: Bi³⁺O(OH)

Daubréeite is a rare bismuth oxyhydroxide, forming tiny, tabular crystals of a creamy-white or yellowish color.

## Characteristics Daubréeite is a mineral from the matlockite group, a bismuth oxyhydroxide. It occurs as very small, thin, tabular crystals, often forming rosette-like or radial aggregates. Its surface can be dull, earthy, or slightly greasy. Due to the small size of the crystals, its macroscopic features are difficult to observe without magnification. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2-2.5, meaning it can be scratched with a fingernail. It has a relatively high density, around 6.4 g/cm³, which is typical for bismuth minerals. The crystals exhibit a greasy or earthy luster and are transparent. ## Colors and Varieties Daubréeite most commonly appears creamy-white, grayish, or yellowish-brown. In transmitted light, it becomes colorless. No named varieties have been distinguished. ## History and Name The mineral was first described in 1876. Its name honors Gabriel Auguste Daubrée (1814-1896), a French geologist, director of the École des Mines in Paris, and a pioneer in experimental geology. ## Uses Daubréeite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or bismuth minerals.

Properties

Mohs hardness: 2-2.5
Luster: Greasy, earthy
Streak: White
Density: 6.4
Cleavage: On {001}
Fracture: Uneven
Transparency: Transparent
Crystal system: Tetragonal

Diagnostic features

## Identification Field identification of daubréeite is practically impossible due to its rarity and the small size of its crystals. In a collection, it can be recognized by its characteristic, tiny, tabular crystals, often in the form of rosettes, and its creamy or yellowish color. Key features include very low hardness, high density, and co-occurrence with other bismuth minerals. ## Distinguishing from Similar Minerals Daubréeite can be confused with other secondary bismuth minerals, such as bismutite or bismoclite. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Crystal Forms Crystals are very small, thin, and tabular, with a square or octagonal outline. They usually form radial or rosette-like aggregates, as well as thin coatings and crusts.

Geological environment

## Genesis Daubréeite is a secondary mineral formed in the oxidation (weathering) zones of ore deposits rich in bismuth. It forms as a result of alterations of primary bismuth minerals, such as native bismuth or bismuthinite. ## Mineral Associations It most commonly co-occurs with native bismuth, bismuthinite, cassiterite, wolframite, and other secondary bismuth minerals like bismutite. ## Localities The most important and type locality is the Constancia mine near Cerro Tazna in Bolivia, from which the best-known specimens originate. This mineral has also been confirmed in several other localities worldwide, including the Clara mine in Germany and in the Czech Republic, but these occurrences are of much lesser collector significance.

Rarity

Very rare

For collectors

## Quality Criteria The most prized daubréeite specimens are those that possess well-formed, though still microscopic, crystals forming distinct, rosette-like aggregates on a contrasting rock matrix. The intensity of the color and the absence of damage to the delicate crystals are also important. Specimens from the type locality (Tazna, Bolivia) are particularly sought after. ## Popular Localities The only source of collector-grade specimens is the historic locality at the Constancia mine in Bolivia. Specimens from other locations are usually microscopic and are of scientific interest only.

Care and storage

## Cleaning Daubréeite specimens are extremely delicate and brittle. Cleaning should be limited to an absolute minimum. If necessary, compressed air can be used to remove loose dust particles. Avoid contact with water and any chemical agents. ## What to Avoid The mineral is very soft and easily susceptible to mechanical damage. Avoid contact with harder minerals, ultrasonic cleaners, acids, and sudden temperature changes. Due to its brittleness, it should be handled with the utmost care. ## Storage It is recommended to store specimens in sealed, padded collector boxes, away from dust, moisture, and direct sunlight. It is best to keep it in a separate compartment to avoid abrasion with other minerals.