Mounanaite
Chemical formula: Pb<sup>2+</sup>Fe<sup>3+</sup><sub>2</sub>(V<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>
Mounanaite is a rare hydroxyl lead iron vanadate, forming characteristic reddish-brown coatings and microcrystals.
Properties
- Mohs hardness
- 3.5
- Luster
- Resinous to earthy
- Streak
- Yellowish-brown
- Density
- 4.87
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Translucent to Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Features facilitating the identification of mounanaite include its characteristic reddish-brown color, earthy or powdery habit, and occurrence environment. The co-occurrence with other rare vanadates, especially in specimens from the type locality, is of key importance. ## Distinguishing from Similar Minerals Mounanaite can be confused with other secondary minerals of similar color, such as goethite or some jarosites. However, goethite has a distinctly different, yellowish-brown streak. Distinguishing it from other rare vanadates (e.g., curienite) is very difficult visually and often requires advanced analytical methods, such as EDS spectroscopy or X-ray diffraction (XRD). ## Crystal Forms The dominant forms of occurrence are earthy, powdery aggregates and crusts. Well-formed crystals are rare and appear as microscopic, thin tablets or blades, often grouped into small, radial or rosette-like aggregates.
Geological environment
## Genesis Mounanaite is a secondary mineral, formed in the oxidation zones of polymetallic (containing uranium, vanadium, and lead) hydrothermal deposits. It forms as a result of weathering and alteration of earlier ore minerals. ## Mineral Associations This mineral most often occurs in association with other secondary vanadates. Its classic associations include francevillite, curienite, chervetite, and vanuralite. It also co-occurs with goethite and manganese oxides. ## Localities The most important and well-known locality in the world is its discovery site – the Mounana mine in Gabon, from which the best specimens originate. This mineral has also been identified in the Carlin gold mine in Eureka County (Nevada, USA).
Rarity
Very rare
For collectors
## Quality Criteria The collector's value of mounanaite primarily depends on its rarity. Specimens rich in the mineral, forming intensely colored, thick crusts on the rock matrix, are most highly prized. Samples with visible, even microscopic, crystals are particularly sought after. The presence of well-formed crystals of associated minerals, especially other rare vanadates from Mounana, adds significant value. ## Popular Localities By far the most valued and classic specimens come from the Mounana mine in Gabon. This is the type locality, which has provided the best quality and quantity of samples of this mineral.
Care and storage
## Cleaning Mounanaite specimens are very delicate and should be handled with care. The safest method for removing dust is to use a soft brush or a photographic air blower. Due to its possible reactivity and softness, wet cleaning, especially with detergents, is not recommended. ## What to Avoid Ultrasonic cleaners, all acids, and chemical agents should be strictly avoided. The mineral is soft and brittle, susceptible to mechanical damage. As a lead mineral, basic precautions must be observed – wash hands after contact with the specimen and avoid inhaling dust. ## Storage It is recommended to store specimens in closed, padded boxes (e.g., micromount type) to protect them from dust and damage. Avoid exposure to moisture and extreme temperatures.