Beudantite Mineral Overview
Mineral name: Beudantite
Mineral class: Sulfate (alunite group)
Known Facts
- Chemical formula: PbFe₃(AsO₄)(SO₄)(OH)₆
- Crystal system: Trigonal
- Mohs hardness: 3.5–4
- Color range: Green, brown, yellow, reddish-brown
- Luster: Vitreous to resinous
- Streak: Pale yellow to white
- Cleavage: Poor
- Fracture: Uneven
- Specific gravity: Approximately 4.3–4.5
- Common locations: Germany, France, United States, Morocco
- Uses: Collector specimens, scientific study
- Similar minerals: Plumbojarosite, corkite, hinsdalite
Physical and Optical Characteristics
Beudantite typically occurs as:
- Small rhombohedral or tabular crystals
- Crusts and coatings
- Granular or earthy aggregates
Crystals are often microscopic to small, and many specimens appear as coatings rather than distinct crystals.
Color varies from green to brown or yellow, sometimes with reddish tones depending on composition and impurities.
The luster is usually vitreous, but can appear resinous or dull in fine-grained material.
Chemical Composition and Structure
Beudantite has the formula:
- PbFe₃(AsO₄)(SO₄)(OH)₆
It is a lead iron arsenate sulfate hydroxide, containing:
- Lead (Pb)
- Ferric iron (Fe³⁺)
- Arsenate (AsO₄³⁻)
- Sulfate (SO₄²⁻)
- Hydroxyl (OH)
It belongs to the alunite group, a family of minerals with similar structures but varying compositions.
Solid solution occurs with related minerals such as:
- Plumbojarosite (sulfate-dominant)
- Corkite (mixed sulfate–phosphate)
Formation and Geological Occurrence
Beudantite forms as a secondary mineral in the oxidation zones of ore deposits, particularly those containing:
- Lead
- Iron
- Arsenic
Typical formation conditions include:
- Weathering of primary sulfide minerals
- Interaction with arsenic- and sulfate-bearing solutions
- Formation in oxidizing, near-surface environments
It is commonly associated with:
- Goethite
- Jarosite-group minerals
- Galena (altered)
- Other secondary arsenates
Common Locations
Notable occurrences of Beudantite include:
- Germany: Classic localities
- France: Type locality (named after François Sulpice Beudant)
- United States: Arizona and other oxidized ore deposits
- Morocco: Secondary mineral assemblages
It is a relatively uncommon mineral, typically found in small quantities.
Uses and Practical Significance
Beudantite has no industrial applications. Its importance lies in:
- Mineral collecting: Especially for collectors of secondary minerals and arsenates
- Scientific study: Understanding oxidation processes in ore deposits
Due to arsenic content, it should be handled with care.
Similar and Related Minerals
Beudantite may be confused with:
- Plumbojarosite: Similar appearance but sulfate-dominant
- Corkite: Contains phosphate instead of arsenate
- Hinsdalite: Another alunite-group mineral with different chemistry
Distinguishing features include:
- Mixed arsenate–sulfate composition
- Association with oxidized lead deposits
- Typically green to brown coloration
Identification Notes for Collectors
- Look for green to brown coatings in oxidized ore zones
- Note association with iron oxides and jarosite-group minerals
- Check for moderate hardness (3.5–4) and resinous luster
- Consider arsenic content—handle carefully
- Use laboratory analysis for confirmation due to similarity with related minerals
Beudantite is a secondary lead iron arsenate sulfate mineral, recognized for its formation in oxidized ore deposits and its place within the alunite group, and is primarily of interest to collectors and mineralogists.