Dussertite

Chemical formula: BaFe₃+₃(As₅+O₄)(As₅+O₃OH)(OH)₆

Dussertite is a rare barium iron arsenate, forming characteristic spherical aggregates of an intense green or yellowish-green color.

## Characteristics Dussertite is a mineral from the arsenate group, belonging to the alunite supergroup. It most commonly occurs as radial or spherulitic (spherical) aggregates, as well as earthy masses or crusts. Well-formed crystals are rare and appear as small, tabular or rhombohedral forms, often gathered in rosettes. Its appearance is very characteristic, especially when it forms spherical aggregates on a contrasting rock matrix. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 3.5. It has a vitreous to resinous luster. It is a rather heavy mineral, which results from the presence of barium in its chemical composition – its density is about 4.3 g/cm³. It is transparent to translucent. ## Colors and Varieties Dussertite occurs in various shades of green and yellow. The most common colors are yellowish-green, grayish-green, grass-green, and also lemon-yellow. No named varieties are distinguished. ## History and Name The mineral was first described in 1925 by the French mineralogist Alfred Lacroix. He named it in honor of Désiré Dussert (1872–1935), a French mining engineer who worked in Algeria and collected the first samples of this mineral. The type locality (locus typicus) is the Djebel Debar mine in Constantine Province, Algeria. ## Uses Dussertite has no industrial applications. However, it is a valued and sought-after collector's mineral due to its rarity, attractive forms of occurrence, and vivid colors.

Properties

Mohs hardness: 3.5
Luster: Vitreous to Resinous
Streak: Pale yellow to greenish-yellow
Density: 4.3-4.39
Cleavage: Good on {0001}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Trigonal

Diagnostic features

## Identification The most characteristic feature of dussertite is its forms of occurrence – spherical, spherulitic aggregates with a radial internal structure. The intense, yellowish-green to green color is also an important clue. High density (perceptible weight relative to size) can aid in identification. ## Distinguishing from Similar Minerals Dussertite can be confused with other secondary green arsenate minerals, such as mimetite, olivenite, or agardite. It is most often distinguished from mimetite by its aggregate form (spherical aggregates instead of hexagonal crystals) and lack of reaction with hydrochloric acid. It differs from olivenite by its lighter shade of green and often radial structure. Accurate differentiation often requires advanced studies, e.g., chemical analysis (EDS). ## Crystal Forms Dussertite crystals, though rare, take the form of small, sharply terminated rhombohedra or thin, hexagonal tablets. However, they usually form dense aggregates, crusts, or characteristic spherical aggregates with a radial internal structure.

Geological environment

## Genesis Dussertite is a secondary mineral formed in the oxidation (weathering) zones of polymetallic ore deposits rich in arsenic and barium. It forms as a result of the alteration of primary minerals containing these elements, such as arsenopyrite or baryte, in the presence of iron-rich solutions. ## Mineral Associations This mineral often co-occurs with other secondary minerals of the oxidation zone. The most common associations include: pharmacosiderite, scorodite, beudantite, goethite, hematite, quartz, as well as baryte and dolomite. ## Localities The most important and historical localities of dussertite are in Algeria (Djebel Debar) and Germany (mines in the Black Forest, e.g., Clara and Michael). It is also known from several locations in Greece (Lavrion mines), France (Duranus), Great Britain (Cornwall), as well as isolated occurrences in the USA (Utah, Nevada) and Australia.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued dussertite specimens are those that exhibit well-formed, spherical aggregates with an intense, vivid, yellowish-green color. Contrast with the rock matrix is important – specimens on light quartz or dark goethite are particularly attractive. The size of the spherulite, its luster, and the absence of mechanical damage significantly increase its collector value. Rare, well-formed crystals, even small ones, are also highly sought after. ## Popular Localities Classic and most prized specimens come from historical localities in Germany, especially from the Clara mine in the Black Forest, which has yielded many world-class specimens. Material from the type locality in Algeria is also considered very valuable. Specimens from Greek Lavrion are also appreciated by collectors.

Care and storage

## Cleaning Dussertite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Due to its arsenic content, avoid inhaling dust during cleaning and wash hands after contact with the mineral. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral. Dussertite is relatively soft and brittle, so it must be protected from impacts and scratches. It should not be heated or exposed to prolonged strong sunlight, which can cause color fading. ## Storage Dussertite specimens are best stored in separate, padded collector boxes to prevent abrasion and mechanical damage. They should be kept in stable conditions, away from moisture and heat sources. Due to the toxicity of arsenic, the mineral should be stored out of reach of children and pets.

Sources

IMA Mineral List (CNMNC)