Fluorwavellite
Chemical formula: Al<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>F·5H<sub>2</sub>O
Fluorwavellite is a hydrated aluminum phosphate that forms characteristic, radial aggregates of acicular crystals.
Properties
- Mohs hardness
- 3.5-4
- Luster
- Vitreous, Pearly
- Streak
- White
- Density
- 2.36
- Cleavage
- Perfect on {010}, Good on {110}
- Fracture
- Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification The key diagnostic feature of fluorwavellite is its characteristic, radial aggregates of acicular crystals. These often form spherical or hemispherical shapes. However, for certain identification, advanced analytical methods such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS) are necessary to distinguish it from the very similar wavellite. ## Distinguishing from Similar Minerals Fluorwavellite is visually indistinguishable from wavellite (Al₃(PO₄)₂(OH)₃·5H₂O). Both minerals form identical shapes and occur in similar environments. The only difference is the dominance of fluorine (F) over hydroxyl groups (OH) in the fluorwavellite structure, which can only be determined by laboratory methods. It may also be confused with other radial zeolites or phosphates, but its unique aggregate form is very suggestive. ## Crystal Forms It occurs as elongated, acicular or prismatic crystals, almost always gathered in radial, spherical, or fan-shaped aggregates.
Geological environment
## Genesis Fluorwavellite is a secondary mineral, forming in the oxidation zones of ore deposits, as well as through low-temperature hydrothermal processes. It forms in rock fissures and cavities, often in sedimentary rocks rich in phosphorus and aluminum, such as cherts and phosphorites, or in altered volcanic rocks. ## Mineral Associations It co-occurs with minerals such as wavellite, quartz, crandallite, wardite, strengite, turquoise, and also with iron and manganese oxides (e.g., goethite, hematite). ## Localities The most important and well-documented occurrences of fluorwavellite worldwide are the type locality – the Silver Coin mine in Humboldt County, Nevada (USA) and Tom's Phosphate Quarry in South Australia. It is also known from several other localities in the USA (e.g., Arkansas) and Australia, where it occurs in phosphatic rocks.
Rarity
Rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, large (for this mineral) and complete radial aggregates. Spheres with sharp, undamaged terminations of acicular crystals are desirable. Intense, though rare, color (e.g., greenish or bluish) and a contrasting substrate (rock matrix) enhance its appeal. Specimens from classic localities, such as the Silver Coin mine, are particularly sought after. ## Popular Localities The most known and prized specimens come from the Silver Coin mine in Nevada, USA, which is the type locality for this mineral. High-quality fluorwavellites are also found in Tom's Phosphate Quarry near Kapunda in South Australia.
Care and storage
## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Brief rinsing in distilled water is permissible, followed by thorough drying. Ultrasonic cleaners should be avoided, as they can damage delicate aggregates. ## What to Avoid The mineral is sensitive to acids and strong bases. Prolonged exposure to moisture and direct sunlight, which can cause fading in some colored specimens, should be avoided. Due to its low hardness, it is susceptible to scratching. ## Storage Fragile fluorwavellite aggregates require storage in separate, padded boxes to prevent mechanical damage. It is best to protect them from dust and sudden temperature changes.