Jamesite
Chemical formula: Pb²⁺₂Zn²⁺Fe³⁺₂(Fe³⁺,Zn²⁺)₄(As⁵⁺O₄)₄(OH)₈(OH,O)₂
Jamesite is a very rare zinc, lead, and iron arsenate, forming aggregates of small, tabular crystals with a characteristic reddish-brown color.
Properties
- Mohs hardness
- 3
- Color
- Reddish brown
- Luster
- Sub-Metallic
- Streak
- Pale brown
- Density
- 0
- Cleavage
- Perfect on {0001}
- Fracture
- Micaceous
- Transparency
- Transparent
- Crystal system
- Triclinic
Diagnostic features
## Identification Jamesite is identified by its unique appearance – reddish-brown, tabular crystals forming rosette-like or fan-like aggregates. Key to identification is its occurrence locality (Tsumeb mine) and co-occurrence with other rare arsenates. Final confirmation requires advanced analytical methods, such as chemical analysis (EDS) and X-ray diffraction (XRD). ## Differentiation from Similar Minerals It can be confused with other arsenates from Tsumeb of similar color, such as hematophanite or ludlockite. Differentiation with the naked eye is practically impossible. Jamesite is distinguished by its specific form of thin, tabular crystals, while other minerals may form different aggregates. Certain identification requires laboratory analysis. ## Crystal Forms Jamesite crystals are very small, thin, and tabular, with a hexagonal outline. They usually occur as radial or fan-like aggregates and rosettes.
Geological environment
## Genesis Jamesite is a secondary mineral that formed in the oxidation zone (gossan) of a mineralized dolomitic deposit. Its formation is a result of the weathering of primary sulfides containing lead, zinc, iron, and arsenic under conditions of high redox potential. ## Mineral Associations This mineral occurs in association with other rare secondary minerals characteristic of the Tsumeb deposit. It most commonly co-occurs with hematophanite, ludlockite, zinc, quartz, anglesite, and getchellite. ## Localities The only confirmed locality of jamesite in the world is its type locality – the Tsumeb mine in the Oshikoto Region, Namibia. It is an endemic mineral to this deposit.
Rarity
Very rare
For collectors
## Quality Criteria The quality of jamesite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates. Most valued are specimens with clearly formed, undamaged rosettes or fans of reddish-brown crystals, well-displayed on a contrasting matrix. The size of the crystals, although always small, also affects the value – larger and better-formed plates are more desirable. Association with other rare minerals from Tsumeb is also important. ## Popular Localities All known and commercially available jamesite specimens originate from a single location – the historic Tsumeb mine in Namibia, which is its type locality. This mine is closed, meaning no new specimens are being acquired, and material on the market comes exclusively from old collections.
Care and storage
## Cleaning Jamesite specimens should be cleaned with utmost care, using only compressed air to remove dust. Due to the presence of arsenic, contact with water and wet cleaning should be avoided to prevent the potential release of toxic compounds. Always wash hands after handling the mineral. ## What to Avoid Contact with acids and other chemicals must be strictly avoided. The mineral is brittle and susceptible to mechanical damage, so ultrasonics, vibrations, and sudden temperature changes should be avoided. As a secondary mineral, it may be sensitive to changes in humidity. ## Storage Jamesite specimens, usually in the form of micromounts, should be stored in stable conditions, in closed, transparent boxes (so-called micromount boxes), which protect them from dust, humidity, and mechanical damage. They should be kept away from direct sunlight and heat sources.