Wilhelmkleinite
Chemical formula: Zn²⁺Fe³⁺₂(As⁵⁺O₄)₂(OH)₂
Wilhelmkleinite is a rare zinc and iron arsenate, forming small, dark green crystals with a strong, almost adamantine luster.
Properties
- Mohs hardness
- 4.5
- Luster
- Adamantine
- Streak
- Green
- Density
- 0
- Cleavage
- On <mi>{23_2}</mi>
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Characteristic features of wilhelmkleinite include its dark green, almost black color, very strong, adamantine luster, and the specific form of small, tabular crystals. A green streak is also an important diagnostic clue. ## Distinguishing from Similar Minerals It can be confused with other dark arsenates from Tsumeb, such as duftite or olivenite. It is distinguished from them by its stronger, adamantine luster and characteristic crystal habit. However, definitive confirmation requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal Forms Wilhelmkleinite forms small, tabular crystals with a pseudo-octahedral habit, often aggregated into radial clusters or small rosettes. Crystals rarely occur individually.
Geological environment
## Genesis Wilhelmkleinite is a secondary mineral, forming in the oxidation zones (gossans) of polymetallic ore deposits rich in arsenic, zinc, and iron. It forms as a result of the weathering of primary sulfides, such as sphalerite and tennantite. ## Mineral Associations This mineral co-occurs with other rare secondary minerals. In its type locality (Tsumeb), it was found in association with kankite, scorodite, köttigite, tsumcorite, ludlockite, leiteite, and quartz. ## Localities The only confirmed and most important occurrence of wilhelmkleinite in the world is its type locality – the Tsumeb mine in the Oshikoto region of Namibia. This is one of the world's most famous mineralogical sites, known for the occurrence of many rare and well-formed minerals.
Rarity
Very rare
For collectors
## Quality Criteria The most prized wilhelmkleinite specimens are those with sharp, well-formed crystals with strong luster, forming aesthetic groups or rosettes. A contrasting, light rock matrix (e.g., quartz) significantly enhances the visual appeal and value of the specimen. Crystal size is crucial – any specimen with crystals exceeding 2-3 mm is considered exceptional. ## Popular Localities The only source of collector's specimens is the historic Tsumeb mine in Namibia. As the mine has been inactive for years, new specimens do not appear on the market, and available ones come exclusively from old collections.
Care and storage
## Cleaning Wilhelmkleinite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its arsenic content, avoid inhaling dust and wash hands after contact with the mineral. Wet cleaning is not recommended. ## What to Avoid Avoid contact with chemicals, especially acids, which can damage the mineral. It should not be heated or subjected to ultrasound. Its brittleness makes it susceptible to mechanical damage. ## Storage Collector's specimens of wilhelmkleinite are best stored in sealed "micromount" boxes, protecting them from dust and damage. It should be kept away from moisture and direct sunlight, although its particular sensitivity to light is not known.