Ferrivauxite
Chemical formula: Fe<sup>3+</sup>Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>3</sub>·5H<sub>2</sub>O
Ferrivauxite is a rare iron and aluminum phosphate, forming aggregates of small, blue-green crystals, prized by systematic mineral collectors.
Properties
- Mohs hardness
- 3
- Luster
- Vitreous
- Streak
- Light green
- Density
- 2.43
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification Ferrivauxite is primarily identified by its characteristic blue-green color, crystal habit (small, tabular or prismatic), and typical radial aggregates. Its occurrence in association with other rare phosphates in hydrothermal veins is also an important indicator. ## Distinguishing from similar minerals It can be confused with other minerals from the vauxite group, such as vauxite or metavauxite. Differentiation often requires advanced chemical (EDS) or crystallographic (XRD) analyses. It differs from vauxite by the dominance of ferric iron over ferrous iron. It can also be confused with turquoise, from which it is much softer and forms differently developed crystals. ## Crystal forms It forms small, tabular crystals with a prismatic habit, often elongated. It is most commonly found in the form of radial or spherulitic aggregates, as well as dense, felted masses covering the surfaces of rock fissures.
Geological environment
## Genesis Ferrivauxite is a secondary mineral, formed in the oxidation zones of ore deposits rich in phosphorus. It forms under low-temperature hydrothermal conditions, crystallizing in fissures and rock cavities. Its formation is associated with the weathering processes of primary phosphate and ore minerals. ## Mineral associations It most commonly co-occurs with other rare phosphates, such as vauxite, metavauxite, wavellite, quartz, cassiterite, and marcasite. The classic association comes from the type locality in Bolivia. ## Localities The most important and historically first occurrence of ferrivauxite is the Siglo XX tin mine in Llallagua, Potosí Department, Bolivia. This is the type locality, from which the world's best specimens of this mineral originate. Other confirmed occurrences are few and do not provide material of collecting significance.
Rarity
Very rare
For collectors
## Quality criteria The most highly prized ferrivauxite specimens are characterized by an intense, saturated blue-green color. The form of crystal development is also important – well-defined, radial aggregates and rosettes are sought after. Crystal size, though usually small, also affects value. Specimens on a light quartz matrix, contrasting with the mineral's color, are particularly attractive. ## Popular localities The only source of valuable collector specimens is the historic locality – the Siglo XX mine in Llallagua, Bolivia. Specimens from this location are considered mineralogical classics and the standard for this species.
Care and storage
## Cleaning Ferrivauxite specimens should be cleaned very carefully, using only distilled water and a soft brush to remove dust. Ultrasonic cleaners should be avoided, as they can damage delicate crystals. ## What to avoid The mineral is sensitive to chemicals, especially acids, which can damage it. Prolonged exposure to strong sunlight, which can cause fading, should be avoided. It is also sensitive to high temperatures, which can lead to dehydration and structural damage. ## Storage Collectible ferrivauxite specimens are best stored in closed boxes or display cases to protect them from dust and mechanical damage. Due to its low hardness, it should not be stored in contact with harder minerals.